secG and Temperature Modulate Expression of Azide-Resistant and Signal Sequence Suppressor Phenotypes of Escherichia coli secA Mutants

ABSTRACT SecA is a dynamic protein that undergoes ATP-dependent membrane cycling to drive protein translocation across the Escherichia coli inner membrane. To understand more about this process, azide-resistant (azi) and signal sequence suppressor (prlD) alleles of secA were studied. We found that azide resistance is cold sensitive because of a direct effect on protein export, suggesting that SecA-membrane interaction is regulated by an endothermic step that is azide inhibitable. secGfunction is required for expression of azide-resistant and signal sequence suppressor activities of azi and prlDalleles, and in turn, these alleles suppress cold-sensitive and export-defective phenotypes of a secG null mutant. These remarkable genetic observations support biochemical data indicating that SecG promotes SecA membrane cycling and that this process is dependent on an endothermic change in SecA conformation.

Genetic analysis ofsulmutants ofEscherichia coliB

SUMMARYThesulgene of B/rw (Witkin) and 26 independently isolatedsulmutants were examined for their suppression of radiation sensitivity. The suppressedlongene was demonstrated by transducing it into a K12proCrecipient. Thesulgene of B/rw and all but one of the B/r mutants was found to be linked to a gene controlling azide resistance. Transduction data established the order of markers asleu azi mutT sul. One B/r mutant was found not transducible with azide resistance,sulmutations were found to suppress the capsular polysaccharide production oflonstrains.