a) Many genes are controlled by sporulation-specific σ factors. For example, σE binds to at least 121 promoters, within 34 operons and 87 individual genes, to regulate more than 250 genes. A loss of this σ factor would prevent the proper transcription of all of these more than 250 genes. The loss of any one of the 121 promoters controlled by this σ factor would only affect the operon or individual gene of that promoter.
b) If we observe carefully at the -35 and -10 sequences from the Figure 11-30b, we will observe that there are differences in these sequences among the genes controlled by the same σ factor. For example, the -35 region of the promoter for the ybaN gene is TTATATT, but the same region for the ydcA gene is TACTATT, yet both still function correctly. When comparing all promoters regulated by a particular σ factor, a “consensus” sequence can be determined, but there will be variations observed as well. Given this, we could not expect all point mutations in this region to effect gene expression. Some variation is possible.