Precursor processing during the maturation of a spore-coat protein in Bacillus megaterium KM.

A protein of apparent mol.wt. 35000 that is extractable from the purified coat fraction of Bacillus megaterium KM spores is synthesized during sporulation as a precursor protein from which a 12-13 amino acid peptide is removed. Cleavage of this small peptide is delayed until 60-90 min after precursor synthesis and is concomitant with the morphological appearance of stage VI. The addition of chloramphenicol, subsequent to precursor synthesis, prevents the appearance of this late processing event. Two-dimensional non-equilibrium pH-gradient gel electrophoresis of the integument extract of forespores isolated at stage V from sporangia pulse-labelled with L-[35S]methionine 1 h before isolation, revealed both unprocessed and processed components. Similar analysis of total protein from the corresponding mother cells revealed only the unprocessed component in relatively small amounts, suggesting that, although the protein may be synthesized in the mother-cell compartment, processing may be restricted to the forespore. Peptide analysis by limited proteolysis was used to examine the relationship between the 35000- and a 17500-mol.wt. coat protein. The possible implications of limited proteolytic processing to maturation of the spore coat are discussed.