A new mutation rpoD800, affecting the sigma subunit of E. coli RNA polymerase is allelic to two other sigma mutants.

TLDR: It is argued that the single locus affected is the structural gene for the sigma subunit of E. coli RNA polymerase, which renders sigma about 10-fold more thermolabile than the wild type sigma at 45°C in vitro.

Abstract: We have characterized a new mutation rpoD800 affecting the sigma gene of E. coli. Upon transfer to high temperature, a strain with the rpoD800 mutation ceases growth within 30 min. We find that this mutation renders sigma about 10-fold more thermolabile than the wild type sigma at 45°C in vitro. We have compared the temperature profile for inactivation of wild type and mutant sigma and find that the mutant inactivates at a temperature about 9° C lower than does the wild type.