Sporulation Phenotype of a Bacillus subtilis Mutant Expressing an Unprocessable but Active σ E Transcription Factor

Abstract

ABSTRACT σ E , a sporulation-specific sigma factor of Bacillus subtilis , is formed from an inactive precursor (pro-σ E ) by a developmentally regulated processing reaction that removes 27 amino acids from the proprotein's amino terminus. A sigE variant ( sigE335 ) lacking 15 amino acids of the prosequence is not processed into mature σ E but is active without processing. In the present work, we investigated the sporulation defect in sigE335 -expressing B. subtilis , asking whether it is the bypass of proprotein processing or a residual inhibition of σ E activity that is responsible. Fluorescence microscopy demonstrated that sigE335 -expressing B. subtilis progresses further into sporulation (stage III) than do strains lacking σ E activity (stage II). Consistent with its stage III phenotype, and a defect in σ E activity rather than its timing, the sigE335 allele did not disturb early sporulation gene expression but did inhibit the expression of late sporulation genes ( gerE and sspE ). The Spo − phenotype of sigE335 was found to be recessive to wild-type sigE . In vivo assays of σ E activity in sigE , sigE335 , and merodiploid strains indicate that the residual prosequence on σ E335 , still impairs its activity to function as a transcription factor. The data suggest that the 11-amino-acid extension on σ E335 allows it to bind RNA polymerase and direct the resulting holoenzyme to σ E -dependent promoters but reduces the enzyme's ability to initiate transcription initiation and/or exit from the promoter.