Small genes under sporulation control in the Bacillus subtilis genome.

Using an oligonucleotide microarray, we searched for previously unrecognized transcription units in intergenic regions in the genome of Bacillus subtilis, with an emphasis on identifying small genes activated during spore formation. Nineteen transcription units were identified, 11 of which were shown to depend on one or more sporulation-regulatory proteins for their expression. A high proportion of the transcription units contained small, functional open reading frames (ORFs). One such newly identified ORF is a member of a family of six structurally similar genes that are transcribed under the control of sporulation transcription factor σ(E) or σ(K). A multiple mutant lacking all six genes was found to sporulate with slightly higher efficiency than the wild type, suggesting that under standard laboratory conditions the expression of these genes imposes a small cost on the production of heat-resistant spores. Finally, three of the transcription units specified small, noncoding RNAs; one of these was under the control of the sporulation transcription factor σ(E), and another was under the control of the motility sigma factor σ(D).