Suppression of asporogeny in Bacillus subtilis. Allele-specific suppression of a mutation in the spoIIA locus.

From a strain carrying spoIIA69, a mutation giving rise to asporogeny, a revertant was isolated which sporulated at about 10(-2) of the wild-type frequency but in which the time-course of sporulation was much protracted. Genetic analysis of this revertant showed that it retained spoIIA69 but had acquired a secondary mutation sas. sas failed to suppress mutations in spoIID, spoIIE or spoIIG; it also failed to suppress another mutation in the spoIIA locus. sas is extremely closely linked (recombination frequency less than or equal to 1%) with the mutation spoIIA69 that it specifically suppresses. Strains carrying sas alone sporulated at a frequency at least two orders of magnitude below that in the spoIIA69 sas double mutant. It is suggested that spoIIA60 and sas lead to compensating amino acid changes in the protein specified by the spoIIA locus.