Genetic evidence that RNA polymerase associated with sigma A factor uses a sporulation-specific promoter in Bacillus subtilis.

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RESUMO

The construction of allele-specific suppressor mutations has enabled us to demonstrate that a sporulation-specific transcription unit in Bacillus subtilis, the spoIIG operon, is transcribed by a form of RNA polymerase associated with sigma A, the principal sigma factor in vegetative cells. The spoIIG operon encodes sporulation-specific factor sigma E, and its transcription is directed from a promoter that is activated about 1 hr after the onset of endospore formation. This promoter contains sequences that are similar to those found at the -10 and -35 regions of promoters that are used by sigma A-associated RNA polymerase, but these sigma A-like recognition sequences are separated by 22 base pairs rather than the typical 17 or 18 base pairs. We have found that substitution of an arginyl residue for the glutamyl residue at position 196 of sigma A (Glu-196----Arg) suppresses the deleterious effect of a thymidine-to-cytidine base substitution at position -11 in the spoIIG promoter. This suppression was allele-specific, since it did not suppress the effects of base substitutions in other positions in the spoIIG promoter or the effects of a thymidine-to-guanosine change at -11. These results support a model in which a form of RNA polymerase containing sigma A is utilized in an unusual manner to activate the transcription of the spoIIG operon well after the onset of endospore formation.

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