Suzanna Bailey

Recurrent mutations in the spliceosome are observed in several human cancers, but their functional and therapeutic significance remains elusive. SF3B1, the most frequently mutated component of the spliceosome in cancer, is involved in the recognition of the branch point sequence (BPS) during selection of the 3' splice site (ss) in RNA splicing. Here, we report that common and tumor-specific splicing aberrations are induced by SF3B1 mutations and establish aberrant 3' ss selection as the most frequent splicing defect. Strikingly, mutant SF3B1 utilizes a BPS that differs from that used by wild-type SF3B1 and requires the canonical 3' ss to enable aberrant splicing during the second step. Approximately 50% of the aberrantly spliced mRNAs are subjected to nonsense-mediated decay resulting in downregulation of gene and protein expression. These findings ascribe functional significance to the consequences of SF3B1 mutations in cancer.

Abstract Activation of the fibroblast growth factor receptor FGFR4 by FGF19 drives hepatocellular carcinoma (HCC), a disease with few, if any, effective treatment options. While a number of pan-FGFR inhibitors are being clinically evaluated, their application to FGF19-driven HCC may be limited by dose-limiting toxicities mediated by FGFR1–3 receptors. To evade the potential limitations of pan-FGFR inhibitors, we generated H3B-6527, a highly selective covalent FGFR4 inhibitor, through structure-guided drug design. Studies in a panel of 40 HCC cell lines and 30 HCC PDX models showed that FGF19 expression is a predictive biomarker for H3B-6527 response. Moreover, coadministration of the CDK4/6 inhibitor palbociclib in combination with H3B-6527 could effectively trigger tumor regression in a xenograft model of HCC. Overall, our results offer preclinical proof of concept for H3B-6527 as a candidate therapeutic agent for HCC cases that exhibit increased expression of FGF19. Cancer Res; 77(24); 6999–7013. ©2017 AACR.

The TREX1 enzyme processes DNA ends as the major 3′ → 5′ exonuclease activity in human cells. Mutations in the TREX1 gene are an underlying cause of the neurological brain disease Aicardi-Goutières syndrome implicating TREX1 dysfunction in an aberrant immune response. TREX1 action during apoptosis likely prevents autoimmune reaction to DNA that would otherwise persist. To understand the impact of TREX1 mutations identified in patients with Aicardi-Goutières syndrome on structure and activity we determined the x-ray crystal structure of the dimeric mouse TREX1 protein in substrate and product complexes containing single-stranded DNA and deoxyadenosine monophosphate, respectively. The structures show the specific interactions between the bound nucleotides and the residues lining the binding pocket of the 3′ terminal nucleotide within the enzyme active site that account for specificity, and provide the molecular basis for understanding mutations that lead to disease. Three mutant forms of TREX1 protein identified in patients with Aicardi-Goutières syndrome were prepared and the measured activities show that these specific mutations reduce enzyme activity by 4–35,000-fold. The structure also reveals an 8-amino acid polyproline II helix within the TREX1 enzyme that suggests a mechanism for interactions of this exonuclease with other protein complexes. The TREX1 enzyme processes DNA ends as the major 3′ → 5′ exonuclease activity in human cells. Mutations in the TREX1 gene are an underlying cause of the neurological brain disease Aicardi-Goutières syndrome implicating TREX1 dysfunction in an aberrant immune response. TREX1 action during apoptosis likely prevents autoimmune reaction to DNA that would otherwise persist. To understand the impact of TREX1 mutations identified in patients with Aicardi-Goutières syndrome on structure and activity we determined the x-ray crystal structure of the dimeric mouse TREX1 protein in substrate and product complexes containing single-stranded DNA and deoxyadenosine monophosphate, respectively. The structures show the specific interactions between the bound nucleotides and the residues lining the binding pocket of the 3′ terminal nucleotide within the enzyme active site that account for specificity, and provide the molecular basis for understanding mutations that lead to disease. Three mutant forms of TREX1 protein identified in patients with Aicardi-Goutières syndrome were prepared and the measured activities show that these specific mutations reduce enzyme activity by 4–35,000-fold. The structure also reveals an 8-amino acid polyproline II helix within the TREX1 enzyme that suggests a mechanism for interactions of this exonuclease with other protein complexes. Processing of DNA ends is an important step in many DNA metabolic pathways such as replication, repair, and recombination. The 3′ → 5′ exonucleases play a critical role in correcting fragmented, modified, mispaired, or even normal nucleotides to generate 3′ termini suitable for downstream events. The drastic consequences that result from impaired 3′ exonuclease activities underscore the importance of these enzymes for cell survival. Proofreading of DNA synthesis by 3′ exonucleases is one of the major determinants of mutagenesis and genome stability and cells lacking this ability show a high incidence of cancers (1Goldsby R.E. Hays L.E. Chen X. Olmsted E.A. Slayton W.B. Spangrude G.J. Preston B.D. Proc. Natl. Acad. Sci. U. S. A. 2002; 99: 15560-15565Crossref PubMed Scopus (142) Google Scholar, 2Goldsby R.E. Lawrence N.A. Hays L.E. Olmsted E.A. Chen X. Singh M. Preston B.D. Nat. Med. 2001; 7: 638-639Crossref PubMed Scopus (135) Google Scholar, 3Longacre A. Sun T. Goldsby R.E. Preston B.D. Storb U. Int. Immunol. 2003; 15: 477-481Crossref PubMed Scopus (12) Google Scholar) (for review, see Ref. 4McElhinny S.A. Pavlov Y.I. Kunkel T.A. Cell Cycle. 2006; 5: 958-962Crossref PubMed Scopus (38) Google Scholar). Cells with defects in proteins containing 3′ exonuclease activity, such as the Werner syndrome protein, MRE11, APE1, and p53 proteins display chromosomal instability, cell cycle checkpoint defects, and sensitivity to ionizing radiation (5Carney J.P. Maser R.S. Olivares H. Davis E.M. Le Beau M. Yates 3rd, J.R. Hays L. Morgan W.F. Petrini J.H. Cell. 1998; 93: 477-486Abstract Full Text Full Text PDF PubMed Scopus (1027) Google Scholar, 6Donehower L.A. Harvey M. Slagle B.L. McArthur M.J. Montgomery Jr., C.A. Butel J.S. Bradley A. Nature. 1992; 356: 215-221Crossref PubMed Scopus (4054) Google Scholar, 7Harvey M. McArthur M.J. Montgomery Jr., C.A. Butel J.S. Bradley A. Donehower L.A. Nat. Genet. 1993; 5: 225-229Crossref PubMed Scopus (492) Google Scholar, 8Stewart G.S. Maser R.S. Stankovic T. Bressan D.A. Kaplan M.I. Jaspers N.G. Raams A. Byrd P.J. Petrini J.H. Taylor A.M. Cell. 1999; 99: 577-587Abstract Full Text Full Text PDF PubMed Scopus (855) Google Scholar, 9Xanthoudakis S. Smeyne R.J. Wallace J.D. Curran T. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 8919-8923Crossref PubMed Scopus (441) Google Scholar). The major 3′ → 5′ exonuclease activity detected in human cell extracts is catalyzed by the TREX1 enzyme. The genes encoding the TREX1 and closely related TREX2 proteins have been identified and cloned (10Hoss M. Robins P. Naven T.J. Pappin D.J. Sgouros J. Lindahl T. EMBO J. 1999; 18: 3868-3875Crossref PubMed Scopus (148) Google Scholar, 11Mazur D.J. Perrino F.W. J. Biol. Chem. 1999; 274: 19655-19660Abstract Full Text Full Text PDF PubMed Scopus (204) Google Scholar), and the recombinant proteins confirm the robust catalytic nature of these enzymes (12Mazur D.J. Perrino F.W. J. Biol. Chem. 2001; 276: 17022-17029Abstract Full Text Full Text PDF PubMed Scopus (117) Google Scholar, 13Perrino F.W. Krol A. Harvey S. Zheng S.L. Horita D.A. Hollis T. Meyers D.A. Isaacs W.B. Xu J. Adv. Enzyme Regul. 2004; 44: 37-49Crossref PubMed Scopus (10) Google Scholar). Amino acid sequence analysis reveals the TREX proteins belong to the DnaQ family of 3′ → 5′ exonucleases; a structurally conserved group of exonucleases that span Archaea and bacteria to humans and includes such proteins as the exonuclease domains of Werner syndrome protein, the bacterial ϵ subunit of DNA polymerase III (ϵ subunit), and exonuclease I (Exo I) 2The abbreviations used are: Exo I, exonuclease I; MBP, maltose-binding protein; PPII, polyproline II; ssDNA, single-stranded DNA; AGS, Acardi-Goutieres syndrome; MES, 4-morpholineethanesulfonic acid. (14Breyer W.A. Matthews B.W. Nat. Struct. Biol. 2000; 7: 1125-1128Crossref PubMed Scopus (83) Google Scholar, 15DeRose E.F. Li D. Darden T. Harvey S. Perrino F.W. Schaaper R.M. London R.E. Biochemistry. 2002; 41: 94-110Crossref PubMed Scopus (26) Google Scholar, 16Hamdan S. Carr P.D. Brown S.E. Ollis D.L. Dixon N.E. Structure (Camb.). 2002; 10: 535-546Abstract Full Text Full Text PDF PubMed Scopus (121) Google Scholar, 17Perry J.J. Yannone S.M. Holden L.G. Hitomi C. Asaithamby A. Han S. Cooper P.K. Chen D.J. Tainer J.A. Nat. Struct. Mol. Biol. 2006; 13: 414-422Crossref PubMed Scopus (123) Google Scholar). A hallmark of the DnaQ family exonucleases is three conserved sequence motifs known as Exo I, II, and III. These motifs contain four conserved acidic residues that participate in coordination of divalent metal ions required for catalysis. The TREX exonucleases are members of a DnaQ family subset that contain a His rather than a Tyr in the ExoIII motif, referred to as the ExoIIIϵ motif (18Barnes M.H. Spacciapoli P. Li D.H. Brown N.C. Gene (Amst.). 1995; 165: 45-50Crossref PubMed Scopus (38) Google Scholar, 19Strauss B.S. Sagher D. Acharya S. Nucleic Acids Res. 1997; 25: 806-813Crossref PubMed Scopus (54) Google Scholar, 20Taft-Benz S.A. Schaaper R.M. Nucleic Acids Res. 1998; 26: 4005-4011Crossref PubMed Scopus (45) Google Scholar). Although the mammalian TREX1 and TREX2 proteins share about 40% amino acid sequence identity, there are distinct structural differences between the two that point to different biological roles for these proteins. The TREX1 protein contains a C-terminal domain of about 75 amino acids that is not present in the TREX2 protein. The amino acid sequences of the C-terminal domains of TREX1 proteins from different mammalian species are moderately conserved, but have no sequence identity to other proteins in the available data base. Additionally, the TREX1 amino acid sequence reveals the presence of a non-repetitive proline-rich region that is also not present in the TREX2 protein. Furthermore, the TREX2 enzymes contain a conserved DNA binding loop positioned adjacent to the active site that has a sequence distinct from the corresponding loop in the TREX1 enzymes. The non-processive autonomous nature of the TREX enzymes suggested that these proteins might serve a proofreading function for one of the multiple human DNA polymerases (10Hoss M. Robins P. Naven T.J. Pappin D.J. Sgouros J. Lindahl T. EMBO J. 1999; 18: 3868-3875Crossref PubMed Scopus (148) Google Scholar). However, Trex1-/- mice show no increase in spontaneous mutation rates but rather display dramatically reduced survival and develop inflammatory myocarditis, indicating a previously unrecognized cellular role for this enzyme (21Morita M. Stamp G. Robins P. Dulic A. Rosewell I. Hrivnak G. Daly G. Lindahl T. Barnes D.E. Mol. Cell. Biol. 2004; 24: 6719-6727Crossref PubMed Scopus (285) Google Scholar). Subsequent work has shown that mutations in the human TREX1 gene at the TREX1/AGS1 locus cause Aicardi-Goutières syndrome (22Crow Y.J. Hayward B.E. Parmar R. Robins P. Leitch A. Ali M. Black D.N. van Bokhoven H. Brunner H.G. Hamel B.C. Corry P.C. Cowan F.M. Frints S.G. Klepper J. Livingston J.H. Lynch S.A. Massey R.F. Meritet J.F. Michaud J.L. Ponsot G. Voit T. Lebon P. Bonthron D.T. Jackson A.P. Barnes D.E. Lindahl T. Nat. Genet. 2006; 38: 917-920Crossref PubMed Scopus (670) Google Scholar), and a genetic mapping study has further shown that the AGS1 locus overlaps with a locus for chilblain lupus, a form of cutaneous lupus erythematosus (23Lee-Kirsch M.A. Gong M. Schulz H. Ruschendorf F. Stein A. Pfeiffer C. Ballarini A. Gahr M. Hubner N. Linne M. Am. J. Hum. Genet. 2006; 79: 731-737Abstract Full Text Full Text PDF PubMed Scopus (102) Google Scholar). These data implicate TREX1 mutations in Aicardi-Goutières syndrome and in systemic lupus erythematosus (22Crow Y.J. Hayward B.E. Parmar R. Robins P. Leitch A. Ali M. Black D.N. van Bokhoven H. Brunner H.G. Hamel B.C. Corry P.C. Cowan F.M. Frints S.G. Klepper J. Livingston J.H. Lynch S.A. Massey R.F. Meritet J.F. Michaud J.L. Ponsot G. Voit T. Lebon P. Bonthron D.T. Jackson A.P. Barnes D.E. Lindahl T. Nat. Genet. 2006; 38: 917-920Crossref PubMed Scopus (670) Google Scholar, 24Alarcon-Riquelme M.E. Nat. Genet. 2006; 38: 866-867Crossref PubMed Scopus (19) Google Scholar, 25Karasinska J.M. Clin. Genet. 2006; 70: 457-461Crossref Scopus (1) Google Scholar), with the of these is likely related to the of DNA and and a aberrant immune response. also that the TREX1 protein, but not in the and to 3′ ends of DNA during cell D. P.J. P. D. J.S. Perrino F.W. J. Mol. Cell. 2006; Full Text Full Text PDF PubMed Scopus Google Scholar). TREX1 shown to function in with the and proteins and to with the protein. the TREX1 exonuclease activity not to by with the protein and the TREX1 protein is not a substrate for A as are the APE1, and proteins. The crystal structure of the human TREX2 protein the dimeric nature of the TREX family exonucleases and the of a human DnaQ family F.W. Harvey S. S. Hollis T. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). in the the active of on for DNA interactions and suggested a mechanism for non-processive catalysis. However, the TREX2 structure determined in the of divalent metal or nucleotides that a understanding of these enzymes with DNA to an to understand the biological and function of this important family of enzymes we have determined the x-ray structures of the TREX1 protein in a substrate with and as a product containing a and to a of The structures important interactions that participate in the of 3′ terminal nucleotide and Additionally, the structure of the non-repetitive proline-rich region within TREX1 suggests a mechanism for interactions with other proteins. and gene encoding amino acids of the human or mouse TREX1 protein as a with the maltose-binding protein a The to a sequence on the of and to the site between the and TREX1 The the of for The cells were to an at and on to with the cells were to for at The protein by acid The protein from the by with at for The protein from the by and and to and at TREX1 mutant were a mutagenesis R. M.A. D.H. J.J. T.J. A to and Scholar), and the were by DNA and protein the or product by protein with in a of or in a of protein at with an of and on a the The and the MES, and nucleotide were at and within to data were in containing for in for were in a loop and in of the belong to group with cell a of the belong to group with cell a TREX1 the of crystal form for and for data and for are in I is the and is the is the as but with of the that were used in protein, I is the and is the is the as but with of the that were used in in a and data were radiation on a and a data were with the D. Biol. 1999; PubMed Scopus Google Scholar). for the data were by molecular the R.J. D. Biol. PubMed Scopus Google Scholar) and a of the human TREX2 protein as a F.W. Harvey S. S. Hollis T. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). The and were the P. Biol. 2004; PubMed Scopus Google Scholar), the structures of the and P.D. P. J.S. J. M. R.J. T. Biol. 1998; PubMed Scopus Google Scholar, Biol. 1997; PubMed Scopus Google Scholar), and the of the structure by P.D. P. J.S. J. M. R.J. T. Biol. 1998; PubMed Scopus Google Scholar). The in the at step in as as the of with the J.M. J. Mol. Biol. 1993; PubMed Scopus Google Scholar) and C. Sci. 1993; PubMed Scopus Google Scholar). The with a of for the and for the x-ray data in the A that than of residues in the have and in the with no residues in the have been for with the TREX1 exonuclease activities of TREX1 enzymes and were measured in substrate as F.W. Harvey S. S. Hollis T. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). were at were determined by the for the human TREX1 ϵ and mouse TREX1 ϵ Structure of the TREX1 a form of the mouse TREX1 protein that amino acids at the in complexes with and recombinant TREX1 protein is and to a of and The TREX1 protein is to form and activity to the protein. S. S. L. S. F. and T. has been shown to to for in the activity of TREX1 (12Mazur D.J. Perrino F.W. J. Biol. Chem. 2001; 276: 17022-17029Abstract Full Text Full Text PDF PubMed Scopus (117) Google Scholar), The structures were determined by molecular the human TREX2 protein as a The an of about of the two TREX1 and a of with for of the residues in the for the nucleotides and two metal ions in also present in the active of structures The and identity of the metal ions by of an that the for the metal ions at a of in The of the TREX1 have been to a of and for the and x-ray data to a of for and complexes. of structures ssDNA, and for nucleotides shown at and of is shown for ions at a of The TREX1 structure the dimeric nature of the exonuclease TREX1 of a with by closely structurally the ϵ subunit and Exo I members of the DnaQ family of 3′ exonucleases data S.E. T. C. J. Mol. Biol. 1995; PubMed Scopus Google Scholar). The TREX1 with other the to form an that the of the as in the TREX2 protein TREX1 has an that of from of with from van and DNA and TREX1 protein in substrate and product complexes. The is bound in the TREX1 active site a of sequence and interactions The of the 3′ nucleotide to the coordination of two divalent metal ions with of and and A of the substrate and product complexes in the protein structure between the two complexes The 3′ nucleotide of the is bound in the as the in the product with a in of the group of the as in the substrate and product complexes of the exonuclease domain of the DNA polymerase I protein T.A. EMBO J. 10: PubMed Scopus Google Scholar). The structures of the substrate and product complexes a nucleotide binding pocket by and helix within the active site that interactions with the and of the 3′ of DNA that in substrate and of terminal nucleotides for The of the bound nucleotide in a between and the of helix The of the nucleotide is positioned by interactions between the 3′ group and the of and a of These specific interactions within the nucleotide binding pocket are the of the TREX1 enzyme to that have 3′ DNA containing a or residues at the 3′ is to by the TREX1 enzyme Res. 2002; PubMed Scopus Google Scholar) such a the of the nucleotide in the binding pocket and prevents catalysis. an nucleotide is to by TREX enzymes not to the interactions of the within the that the terminal nucleotide in the for of 3′ nucleotides by the TREX enzymes to in a of ability to with The high of TREX1 and TREX2 for with other DnaQ exonucleases such as ϵ H. A. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar, H. Perrino F.W. Biochemistry. 1996; PubMed Scopus Google Scholar), has been to a loop between and adjacent to the active that contains conserved residues (12Mazur D.J. Perrino F.W. J. Biol. Chem. 2001; 276: 17022-17029Abstract Full Text Full Text PDF PubMed Scopus (117) Google Scholar, F.W. Harvey S. S. Hollis T. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). the human TREX2 protein the loop contains shown to to DNA binding and of of the to the for DNA of TREX2 by about and as as three are the corresponding loop in TREX1 has a conserved and the of TREX1 for single-stranded DNA is about than that of the TREX2 protein with measured for the two enzymes (12Mazur D.J. Perrino F.W. J. Biol. Chem. 2001; 276: 17022-17029Abstract Full Text Full Text PDF PubMed Scopus (117) Google Scholar). are for this The is that there are other residues the loop in the TREX1 protein to DNA A of the TREX1 and TREX2 protein structures that TREX1 at the of the active to participate in DNA binding interactions with the and of the 5′ that is in a Although the is with the interactions with the or of and might to DNA to provide single-stranded substrate for the enzyme active The corresponding in the TREX2 protein is has a and is to participate in interactions with the for the differences between TREX1 and TREX2 in DNA binding might result from differences during the DNA binding The DNA binding loop in TREX2 to on the of in the structure for residues the F.W. Harvey S. S. Hollis T. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). in the TREX1 structure of the loop is the of the loop containing the conserved is present in the DNA binding an of this the region containing the residues the of binding might for TREX1 as with TREX1 that the TREX1 enzyme in the a for to understand TREX1 protein interactions D. P.J. P. D. J.S. Perrino F.W. J. Mol. Cell. 2006; Full Text Full Text PDF PubMed Scopus Google Scholar). of the TREX1 protein structure is a polyproline II helix by a non-repetitive proline-rich region that contains within an 8-amino acid The of crystal structures of proteins containing with than is are that are to J. PubMed Scopus Google Scholar). The of residues in is the the helix of the other about on the of the of the the TREX enzymes and DnaQ exonucleases this motif is to the TREX1 protein with the corresponding region in the TREX2 enzyme a proline-rich sequences are in many proteins and are to function as for such as for a conserved and domains A. W.A. Sci. 2003; Google Scholar). These interactions are than one proline-rich region for The of the two on the of the for interactions with two of these the active and is likely to a of for the TREX1 protein. interactions between the TREX1 and proteins might that the protein contains one or of the proline-rich region important protein for the TREX proteins is the on conserved residues at the has been that the dimeric structure of TREX exonucleases is conserved species that this enzyme F.W. Harvey S. S. Hollis T. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). suggests that the dimeric nature of the protein a critical role in biological or mice display in that a role for this enzyme in of DNA termini during a subset of or recombination. The for of two DNA termini to or other DNA might have the of a dimeric structure of the with active on of the the enzyme the of two 3′ TREX1 and by (22Crow Y.J. Hayward B.E. Parmar R. Robins P. Leitch A. Ali M. Black D.N. van Bokhoven H. Brunner H.G. Hamel B.C. Corry P.C. Cowan F.M. Frints S.G. Klepper J. Livingston J.H. Lynch S.A. Massey R.F. Meritet J.F. Michaud J.L. Ponsot G. Voit T. Lebon P. Bonthron D.T. Jackson A.P. Barnes D.E. Lindahl T. Nat. Genet. 2006; 38: 917-920Crossref PubMed Scopus (670) Google Scholar) mutations cause Acardi-Goutieres syndrome the of these specific mutations on the TREX1 distinct mutations within the TREX1 gene were identified as the underlying cause of (22Crow Y.J. Hayward B.E. Parmar R. Robins P. Leitch A. Ali M. Black D.N. van Bokhoven H. Brunner H.G. Hamel B.C. Corry P.C. Cowan F.M. Frints S.G. Klepper J. Livingston J.H. Lynch S.A. Massey R.F. Meritet J.F. Michaud J.L. Ponsot G. Voit T. Lebon P. Bonthron D.T. Jackson A.P. Barnes D.E. Lindahl T. Nat. Genet. 2006; 38: 917-920Crossref PubMed Scopus (670) Google Scholar), and a form of systemic lupus chilblain lupus, is also known to to the genetic locus (23Lee-Kirsch M.A. Gong M. Schulz H. Ruschendorf F. Stein A. Pfeiffer C. Ballarini A. Gahr M. Hubner N. Linne M. Am. J. Hum. Genet. 2006; 79: 731-737Abstract Full Text Full Text PDF PubMed Scopus (102) Google Scholar). is a neurological brain disease that many with and systemic lupus erythematosus J. F. 15: PubMed Scopus Google Scholar). also closely of in F. Full Text Full Text PDF PubMed Scopus Google Scholar). of the identified mutations in the TREX1 gene or proteins at amino acids and are three are point mutations in to His to and an of at The and residues are conserved in known TREX1 To provide the molecular for this we used mouse TREX1 structure in with of human and mouse TREX1 enzymes to understand the consequences of these mutations on the TREX1 protein The exonuclease activities of the three mutant TREX1 proteins were reduced for the human and mouse proteins to the mutation the in activity with a for the human protein for the mutation of a in activity for the is adjacent to the active site in the helix that contains two conserved catalytic and The in the activities of and is likely to the that the mutation the helix and prevents of the catalytic residues for nucleotide the mutation is by the of in a of the human TREX1 exonuclease activity with enzyme for the at the TREX1 with two of the to would these and the Although the mutation is from the active site the in activity by this mutation a further that the dimeric nature of the TREX1 enzyme is required for catalytic of TREX1 enzymes for human and mouse enzymes were determined from containing the of TREX1 between and and were on and as previously F.W. Harvey S. S. Hollis T. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). mutation is the of an at amino acid for is of of activity TREX1 is of of activity TREX1 in a The in catalytic activities these three mutant forms of TREX1 that human The exonuclease activity measured in for the TREX1 mutation that a in TREX1 activity is to the neurological in the with the in activity of the TREX1 mutation indicating an TREX1 These data that the high of activity for this enzyme (10Hoss M. Robins P. Naven T.J. Pappin D.J. Sgouros J. Lindahl T. EMBO J. 1999; 18: 3868-3875Crossref PubMed Scopus (148) Google Scholar, D.J. Perrino F.W. J. Biol. Chem. 2001; 276: 17022-17029Abstract Full Text Full Text PDF PubMed Scopus (117) Google Scholar, F.W. Harvey S. S. Hollis T. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar) has been and even in the activity have multiple to the in patients TREX1 mutations that might catalytic activity or the ability of TREX1 to with cellular to an in with