EVIDENCE THAT THE SPOIIM GENE OF BACILLUS-SUBTILIS IS TRANSCRIBED BY RNA-POLYMERASE ASSOCIATED WITH SIGMA(E)

We have investigated the temporal and spatial regulation of spoIIM, a gene of Bacillus subtilis whose product is required for complete septu m migration and engulfment of the forespore compartment during sporula tion. The spoIIM promoter was found to become active about 2 h after t he initiation of sporulation. The effects of mutations on the expressi on of a spoIIM-lacZ fusion were most consistent with its utilization b y sigma(E)-associated RNA polymerase (Esigma(E)). A unique 5' end of t he in vivo spoIIM transcript was detected by primer extension analysis and was determined to initiate at the appropriate distance from a seq uence conforming very closely to the consensus for genes transcribed b y Esigma(E). A partially purified preparation of Esigma(E) produced a transcript in vitro that initiated at the same nucleotide as the prime r extension product generated from in vivo RNA. Ectopic induction of s igma(E) synthesis during growth resulted in the immediate and strong e xpression of a spoIIM-lacZ fusion, but an identical fusion was complet ely unresponsive to induced synthesis of either sigma(F) or sigma(G) u nder similar conditions. The results of plasmid integration-excision e xperiments in which the NpoIIM gene was reversibly disrupted by a temp erature-sensitive integrational vector suggested that spoIIM expressio n is required in the forespore compartment, but direct examination of subcellular fractions enriched for mother cell or forespore material i ndicated that spoIIM expression cannot be confined to the forespore. W e conclude that spoIIM is a member of the sigma(E) regulon and that it may be transcribed exclusively by Esigma(E). We discuss the implicati ons of this conclusion for models in which activation of sigma(E) in t he mother cell is proposed to be a part of the mechanism responsible f or initiating separate programs of gene activity in the two sporangium compartments.