Identification of distinct messenger RNAs for nuclear lamin C and a putative precursor of nuclear lamin A.The lamins are the major components of the nuclear matrix and are known as lamins A, B, and C with Mr 72,000, 68,000, and 62,000 when analysed by SDS PAGE. These three polypeptides are very similar, as determined by polypeptide mapping and immunological reactivity. Lamins A and C are so homologous that a precursor-product relationship has been proposed. Using an antiserum against nuclear matrix proteins that specifically immunoprecipitates the three lamins, we examined their synthesis in the rabbit reticulocytes lysate. Four bands of Mr 62,000, 68,000, 70,000, and 74,000 were specifically immunoprecipitated when polysomes or polyadenylated RNA were translated in vitro. By two-dimensional gel electrophoresis, the 68,000- and the 62,000-mol-wt proteins were identified as lamins B and C, respectively, and the 74,000-mol-wt polypeptide had properties of a precursor of lamin A. The mRNAs of lamin C and of the putative precursor of lamin A were completely separated by gel electrophoresis under denaturing conditions, and their respective sizes were determined. These results suggest that lamin A is not a precursor of lamin C.
TRiC-P5, a novel TCP1-related protein, is localized in the cytoplasm and in the nuclear matrixWe have recently reported the cloning of a novel protein, TRiC-P5, with significant homology with protein 1 of the t-complex (TCP1). In the present study, the cellular localization of TRiC-P5 in Raji cells has been determined using an antiserum raised against a 18.5 kDa fusion protein. Results from cell fractionation and immunoblot studies indicate that TRiC-P5 is mainly localized in the cytoplasm. In addition, a significant part of TRiC-P5 is also found in the nucleus where it is attached to the nuclear matrix, a complex filament network involved in essential cellular functions such as DNA replication, and RNA transcription and maturation. Immunofluorescence experiments using the anti-TRiC-P5 antibodies confirm these results. We also provide evidence that, in the cytoplasm, TRiC-P5 is part of a large protein complex, most probably the TCP1-ring complex (TRiC), a hetero-oligomeric ring complex that plays a role of molecular chaperone in the folding of actin and tubulin.
DNA-binding Proteins of Herpes Simplex Virus Type 1-infected BHK Cell Nuclear MatricesThe nuclear matrix is involved in the replicative cycle of herpes simplex virus type 1 (HSV-1) and in at least some cases viral DNA has been shown to be closely associated with this structure. In this communication, we report the presence of five DNA-binding proteins in the nuclear matrix of HSV-1-infected BHK cells. These proteins (p114, p89, p77, p37 and p29) were detected by probing with 32P-labelled HSV DNA after Western blotting of nuclear matrix proteins. Three were identified as virion components: p89 as VP12, p77 as VP13 and p37 as the capsid protein VP22a. These polypeptides were detected in cells and nuclei and found to be associated with the nuclear matrix late during the lytic cycle, long after the onset of viral DNA replication. The nuclear matrix-binding capacity of VP22a depended on viral DNA replication, since after DNA polymerase inhibition it was still synthesized and transported into the nucleus but was no longer associated with the nuclear matrix. After inhibition of viral DNA synthesis, VP13 was no longer found in cells, nuclei or nuclear matrices. These results suggest a possible involvement in anchoring viral progeny DNA to the nuclear matrix.