Mutation affecting thermostability of sigma subunit of Escherichia coli RNA polymerase lies near the dnaG locus at about 66 min on the E. coli genetic map.

The Escherichia coli strain, ts-rnp5, originally described in 1975 by G. D. Burdick and H. Berger, is shown to possess an RNA polymerase (RNA nucleotidyltransferase) sigma subunit with an activity 4--6 times less thermostable at 45 degrees than sigma from wild-type strains. This defect remains associated with the sigma polypeptide through a variety of purification stages, including renaturation of sigma after its elution from sodium dodecyl sulfate/polyacrylamide gels. The mutation responsible for decreased thermostability of sigma, called rpoD1, cotransduces with dnaG and therefore is located at about 66 min of the E. coli genetic map.