title: R-factor mutant capable of specifying hypersynthesis of penicillinase.
abstract: The physical characteristics of a mutant, R(M201-2), capable of conferring high and stable ampicillion resistance was analyzed. The R(M201-2) and its parent R-factor deoxyribonucleic acid (DNA) could be isolated as an extrachromosomal and covalently closed circular form. Their buoyant densities were both 1.712 g/cm(3), and their molecular weights were about 82 x 10(6) and 64 x 10(6), respectively, when measured by CsCl and sucrose density gradient analyses. The contour lengths by electron microscopy were 35.9 +/- 0.6 and 31.0 +/- 0.6 mum, respectively. By using the extracted R-factor DNA, the mutant and parent characters were transformable to another Escherichia coli strain. The mutant R factor showed an increased amount of DNA even after conjugal transfer to Proteus. An increase in the size of R-factor DNA was thus considered to be the cause of the high level of ampicillin resistance.
mesh_terms: D000667:Ampicillin / Q000494:pharmacology; D002250:Carbon Radioisotopes; D002499:Centrifugation, Density Gradient; D003227:Conjugation, Genetic; D004269:DNA, Bacterial; D004270:DNA, Circular / Q000032:analysis; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology*; D005111:Extrachromosomal Inheritance; D005796:Genes; D008854:Microscopy, Electron; D008970:Molecular Weight; D009154:Mutation; D010403:Penicillin Resistance; D010405:Penicillinase / Q000096:biosynthesis*; D011513:Proteus mirabilis / Q000187:drug effects; D013936:Thymidine; D014170:Transformation, Genetic; D014316:Tritium
chemical_list: D002250:Carbon Radioisotopes; D004269:DNA, Bacterial; D004270:DNA, Circular; D014316:Tritium; D000667:Ampicillin; D010405:Penicillinase; D013936:Thymidine