title: Temperature-sensitive chloramphenicol acetyltransferase from Escherichia coli carrying mutant R factors.
abstract: Bacteria carrying temperature-sensitive mutant R factors for chloramphenicol resistance were isolated. In the presence of chloramphenicol, these bacteria grew at 34 C but not at 43 C. The mutations in the chloramphenicol resistance gene of the R factors affected neither the resistance of the bacteria to dihydrostreptomycin and tetracycline nor the stability of the R factors at 43 C. The chloramphenicol acetyltransferase obtained from Escherichia coli K-12 carrying the mutant R factors was heat-labile as compared with that from a strain carrying the wild-type R factor. We could not find chloramphenicol acetyltransferase activity in 17 chloramphenicol-sensitive and 5 -resistant strains (selected in vitro) of E. coli examined. The results strongly suggest that the chloramphenicol resistance gene of the R factors is the structural gene of the chloramphenicol acetyltransferase rather than the genome controlling the expression of a chromosomal determinant for the enzyme. Furthermore, the studies confirm that the existence of the chloramphenicol acetyltransferase is the primary cause of chloramphenicol resistance of bacteria carrying the R factor. Both the enzyme activity producing the monoacetyl derivative from chloramphenicol and the subsequent formation of the diacetate from the monoacetyl product were heat-labile to the same degree. The results suggest that only one enzyme participates in two steps of chloramphenicol acetylation.
mesh_terms: D000217:Acyltransferases; D002247:Carbon Isotopes; D002701:Chloramphenicol / Q000494:pharmacology; D004352:Drug Resistance, Microbial; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology*; D005111:Extrachromosomal Inheritance; D005827:Genetics, Microbial; D009154:Mutation
chemical_list: D002247:Carbon Isotopes; D002701:Chloramphenicol; D000217:Acyltransferases