Stanley N. Cohen

Construction and characterization of a class of multicopy plasmid cloning vehicles containing the replication system of miniplasmid P15A are described. The constructed plasmids have cleavage sites within antibiotic resistance genes for a variety of commonly employed site-specific endonucleases, permitting convenient use of the insertional inactivation procedure for the selection of clones that contain hybrid DNA molecules. Although the constructed plasmids showed DNA sequence homology with the ColE1 plasmid within the replication region, were amplifiable by chloramphenicol or spectinomycin, required DNA polymerase I for replication, and shared other replication properties with ColE1, they were nevertheless compatible with ColE1. P15A-derived plasmids were not self-transmissible and were mobilized poorly by Hfr strains; however, mobilization was complemented by the presence of a ColE1 plasmid within the same cell.

BACKGROUND: Carotid-artery stenting and carotid endarterectomy are both options for treating carotid-artery stenosis, an important cause of stroke. METHODS: We randomly assigned patients with symptomatic or asymptomatic carotid stenosis to undergo carotid-artery stenting or carotid endarterectomy. The primary composite end point was stroke, myocardial infarction, or death from any cause during the periprocedural period or any ipsilateral stroke within 4 years after randomization. RESULTS: For 2502 patients over a median follow-up period of 2.5 years, there was no significant difference in the estimated 4-year rates of the primary end point between the stenting group and the endarterectomy group (7.2% and 6.8%, respectively; hazard ratio with stenting, 1.11; 95% confidence interval, 0.81 to 1.51; P=0.51). There was no differential treatment effect with regard to the primary end point according to symptomatic status (P=0.84) or sex (P=0.34). The 4-year rate of stroke or death was 6.4% with stenting and 4.7% with endarterectomy (hazard ratio, 1.50; P=0.03); the rates among symptomatic patients were 8.0% and 6.4% (hazard ratio, 1.37; P=0.14), and the rates among asymptomatic patients were 4.5% and 2.7% (hazard ratio, 1.86; P=0.07), respectively. Periprocedural rates of individual components of the end points differed between the stenting group and the endarterectomy group: for death (0.7% vs. 0.3%, P=0.18), for stroke (4.1% vs. 2.3%, P=0.01), and for myocardial infarction (1.1% vs. 2.3%, P=0.03). After this period, the incidences of ipsilateral stroke with stenting and with endarterectomy were similarly low (2.0% and 2.4%, respectively; P=0.85). CONCLUSIONS: Among patients with symptomatic or asymptomatic carotid stenosis, the risk of the composite primary outcome of stroke, myocardial infarction, or death did not differ significantly in the group undergoing carotid-artery stenting and the group undergoing carotid endarterectomy. During the periprocedural period, there was a higher risk of stroke with stenting and a higher risk of myocardial infarction with endarterectomy. (ClinicalTrials.gov number, NCT00004732.)

Transformation of E. coli cells treated with CaCl(2) to multiple antibiotic resistance by purified R-factor DNA is reported. Drug resistance is expressed in a small fraction of the recipient bacterial population almost immediately after uptake of DNA, but full genetic expression of resistance requires subsequent incubation in drugfree medium before antibiotic challenge. Transformed bacteria acquire a closed circular, transferable DNA species having the resistance, fertility, and sedimentation characteristics of the parent R factor. Covalently-closed, catenated, and open (nicked) circular forms of R-factor DNA are all effective in transformation, but denaturation and sonication abolish the transforming ability of R-factor DNA in this system.

The construction of new plasmid DNA species by in vitro joining of restriction endonuclease-generated fragments of separate plasmids is described. Newly constructed plasmids that are inserted into Escherichia coli by transformation are shown to be biologically functional replicons that possess genetic properties and nucleotide base sequences from both of the parent DNA molecules. Functional plasmids can be obtained by reassociation of endonuclease-generated fragments of larger replicons, as well as by joining of plasmid DNA molecules of entirely different origins.