Characterization and function of intracellular proteases in sporulating Bacillus cereus

Intracellular proteases from sporulating Bacillus cereus have been purified by ammonium sulfate fractionation, heat treatment and DEAE cellulose column chromatography. After the last purification step, two protease activities, with an activity ratio of about thirty to one are resolved. Both proteases are resistant to o-phenanthroline but sensitive to phenyl methyl sulfonyl fluoride. Their separation by polyacrylamide gel electrophoresis and DEAE cellulose column chromatography, their difference in heat sensitivity and a mutation affecting only the major intracellular protease (IP1) suggest that the two are products of distinct genes. An IP1 mutant previously shown to produce coat defective spores (4) also turnsover protein with a reduced rate during late sporulation stages. Correlated with the slower turnover rate in this mutant is the more rapid disappearance of IP1. A partial revertant of this mutant has a protein turnover rate intermediate between that of the original mutant and wild type. These correlations imply that IP1 has an important role in protein turnover during sporulation.