Abstract
A set of F'' strains of E. coli K-12 partially diploid for various chromosomal segments was examined for possible gene dosage effects in the synthesis of .sigma. factor of the DNA-dependent RNA polymerase (RNA nucleotidyltransferase; nucleoside-triphosphate:RNA nucleotidyltransferase, EC 2.7.7.6). All F'' strains diploid for the dnaG region synthesize .sigma. at rates 2-3 times higher than other F'' or F- strains. Salmonella typhimurium strains harboring these F'' produce E. coli .sigma. besides Salmonella .sigma., since Salmonella .sigma. can be precipitated with antiserum against E. coli RNA polymerase but is distinguishable from E. coli .sigma. in its mobility in sodium dodecyl sulfate/polyacrylamide gel electrophoresis. E. coli .sigma. polypeptides thus produced seem to be stable in S. typhimurium cells. A structural gene for .sigma. (rpoD) is apparently located at the metC-argG region, probably near the dnaG locus (66 min on the current genetic map of E. coli).