title: The hsd (host specificity) genes of E. coli K 12.
abstract: The hsd genes of E. coli K 12 have been cloned in phage lambda by a combination of in vitro and in vivo techniques. Three genes, whose products are required for K-specific restriction and modification, have been identified by complementation tests as hsdR, M and S. The order of these closely linked genes was established as R, M, S by analysis of the DNA of genetically characterised deletion derivatives of lambda hsd phages. The three genes are transcribed in the same direction but not necessarily as a single operon. Genetic evidence identifies two promoters, one from which transcription of hsdM and S is initiated and a second for the hsdR gene. The hsdR gene codes for a polypeptide of molecular weight approximately 130 000; hsdM for one of 62--65 000 and the hsdS gene was associated with two polypeptides of approximately 50 000. Circumstantial evidence suggest that one of these two polypeptides may be a degradation, or processed, derivative of the other. The hsdS polypeptide of E. coli B has a slightly higher mobility in an SDS-polyacrylamide gel than does that of E. coli K 12. A probe comprising most of the hsdR gene and all of the hsdM and S genes of E. coli K 12 shares extensive homology with the DNA of E. coli B but none with that of E. coli C.
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D010582:Bacteriophage lambda / Q000235:genetics; D003001:Cloning, Molecular; D004262:DNA Restriction Enzymes / Q000235:genetics*; D004792:Enzyme Precursors / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics*; D005796:Genes; D005822:Genetic Vectors; D008970:Molecular Weight; D009876:Operon; D013045:Species Specificity; D013379:Substrate Specificity; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D004792:Enzyme Precursors; D004262:DNA Restriction Enzymes