Evidence for an Additional Temporal Class of Gene Expression in the Forespore Compartment of Sporulating Bacillus Subtilis

We present evidence indicating that the previously studied, sporulation-induced gene 0.3 kb, which encodes a stable RNA present at late developmental stages, is transcribed in the forespore chamber of sporulating cells of Bacillus subtilis. Compartmentalized gene expression was demonstrated on the basis of subcellular fractionation experiments in which severalfold-higher levels of 0.3 kb-directed beta-galactosidase specific activity were observed in forespore extracts than in extracts from the mother cell and dependence studies in which 0.3 kb transcription was found to be blocked in mutants bearing mutations in spoIIIA, spoIIIE, and spoIIIG, genes which are known to govern forespore gene expression. Also, 0.3 kb transcription could be switched on during growth in cells in which transcription of the forespore regulatory gene spoIIIG was engineered to be activated in response to the lac inducer IPTG (isopropyl-beta-D-thiogalactopyranoside). Although it is transcribed in the forespore, 0.3 kb is switched on at a later developmental stage than other previously studied forespore-expressed genes, and hence it appears to be representative of an additional temporal class of compartmentalized gene expression.