The mother-cell line of gene expression during sporulation in Bacillus subtilis is a hierarchical cascade consisting of at least four temporally controlled gene sets, the first three of which each contain a regulatory gene for the next gene set in the pathway. gerE, a member of the penultimate gene set, is a regulatory gene whose products is required for the transcriptional activation of genes (coat protein genes cotB and cotC) in the last gene set. The gerE product also influences the expression of other members of the penultimate gene set (coat protein genes cotA and cotD appear to be repressed and activated, respectively). We now report that the purified product of gerE (GerE) is a DNA-binding protein that adheres to the promoters for cotB and cotC. We also show that GerE stimulates cotB and cotC transcription in vitro by RNA polymerase containing the mother-cell sigma factor sigma K. These findings support the view that GerE is a positively acting, regulatory protein whose appearance at a late stage of development directly activates the transcription of genes in the last known temporal class of mother-cell-expressed genes. In addition, GerE stimulates cotD transcription and inhibits cotA transcription in vitro by sigma K RNA polymerase, as expected from in vivo studies, and, unexpectedly, profoundly inhibits in vitro transcription of the gene (sigK) that encodes sigma K. The effects of GerE on cotD and sigK transcription are just the opposite of the effects exerted by the earlier-appearing, mother-cell regulatory protein spoIIID, suggesting that the ordered appearance of first SpoIIID, then GerE, ensures proper flow of the regulatory cascade controlling gene expression in the mother cell.