Switch Protein Alters Specificity of RNA Polymerase Containing a Compartment-Specific Sigma Factor

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Abstract
During sporulation in Bacillus subtilis , expression of developmental genes spoIVCB and cotD is induced in the mother cell compartment of the sporangium at morphological stages IV and V, respectively. A 27-kilodalton RNA polymerase sigma factor called σ K (or σ 27 ) has been found that causes weak transcription of spoIVCB and strong transcription of cotD . A 14-kD protein was also discovered that changes the specificity of σ K -containing RNA polymerase, greatly stimulating spoIVCB transcription and markedly repressing cotD transcription. Both σ K and the 14-kD protein are products of genes known to be required for expression of specific genes in the mother cell. Thus, σ K directs gene expression in the mother cell and it is proposed that inactivation or sequestering of the 14-kD protein switches the temporal pattern of gene expression during the transition from stages IV to V of development.