Variation in RNA polymerase sigma subunit composition within different stocks of Escherichia coli W3110

The composition of RNA polymerase sigma subunits was analyzed for stock strains of Escherichia coli K-12 W3110 in Japan. Heterogeneity was discovered with respect to two sigma subunits, sigma(28) (sigma(F), the rpoF gene product) and sigma(38) (sigma(S), the rpoS gene product). Five different types of W3110 were identified: A-type lineages have both a subunits in intact forms; B-type lineages carry a truncated sigma(38) subunit and an intact sigma(28) subunit; C-type lineages carry an intact sigma(28) subunit but lack a sigma(38) subunit; D-type lineages have only a sigma(38) subunit without a sigma(28) subunit; and E-type stocks lack both sigma subunits. All the lineages examined, however, contain the intact forms of sigma(70) (sigma(D), the rpoD gene product) and sigma(54) (sigma(N), the rpoN gene product). As expected from the lack of a sigma(28) subunit, cells of D- and E-type lineages are nonmotile. The truncated form of the sigma(38) subunit in B-type stocks carries two mutations near its N terminus and lacks C-terminal proximal region 4 due to an amber mutation. The failure of C- and E-type W3110 cells to express sigma(38) and that of D- and E-type cells to express sigma(28) were found to be due to defects in transcription even though the respective a subunit genes remain intact. These findings emphasize the importance of paying attention to possible variations in the genetic background between laboratory stocks originating from the same strain.