An unusually small gene required for sporulation by Bacillus subtilis

We report the cloning and characterization of an unusually small gene called spoVM whose product is required for normal formation of the cortex and coat during sporulation in Bacillus subtilis. The spoVM gene is adjacent to, and in convergent orientation with, the B. subtilis homologue to the Escherichia coli gene for ribosomal protein L28. The spoVM open reading frame is only 26 codons in length and is capable of encoding a polypeptide of 3 kDa. The short length of spoVM was verified by means of complementation experiments with wild-type and deletion-mutated copies of the open reading frame and by engineering the synthesis of the spoVM gene product in E. coli. Transcription of spoVM was induced during the second hour of sporulation (approximately stage II) by the appearance of the sporulation RNA polymerase sigma factor, sigma E. Efficient transcription of spoVM additionally required the action of the sporulation DNA-binding protein SpoIIID. Because spoVM was not strongly required for the transcription of several genes expressed at late times in development, its protein product is likely to play a morphogenetic rather than a regulatory role in sporulation.