The Major Acid-soluble Proteins of Bacillus subtilis Spores: Partial Amino Acid Sequence and Forespore Location of Their mRNAs

SUMMARY: In Bacillus subtilis the α, β, γ and δ components comprise 80–90% of the total acid-soluble spore proteins (ASSPs). Sequence analysis demonstrates that α and β share 32 of their first 36 amino acids and are closely related to the A and C ASSPs of Bacillus megaterium spores, confirming the results of analysis of their cloned genes. Despite the difference in apparent size of γ and δ, they have identical N-terminal sequences (37 residues). Unless γ and δ derive from very recently duplicated genes, it appears that γ is derived from δ, either in vivo or during isolation. Although the sequenced regions of γ and δ have no homology to α and β, outside of the previously recognized pentapeptide recognition sequence for the spore endopeptidase, they share 10 and 15 residue peptides flanking this sequence with ASSP B of B. megaterium, but in reverse order. At least two groups of ASSPs have, therefore, been conserved between B. subtilis and B. megaterium: the multigene ACαβ family and the Bγ(δ) group. Sequence conservation in each group implies selection for functions in addition-to storage. Both the α and β components of B. subtilis ASSPs and their mRNAs are located in the forespore compartment of cells at t 5·5 of sporulation, the time of most rapid ASSP synthesis. The sizes of these transcripts (250–350 bp) and their ability to direct the in vitro synthesis of ASSPs of mature size, indicate that genes for these ASSPs are monocistronic, consistent with dispersed map location. Synthesis of ASSPs is, therefore, coordinately controlled by selective transcription in the forespore.