Exchange of precursor-specific elements between pro-sigma(E) and pro-sigma(K) of Bacillus subtilis

sigma(E) and sigma(K) are sporulation-specific sigma factors of Bacillus subtilis that are synthesized as inactive proproteins. Pro-sigma(E) and pro-sigma(K) are activated by the removal of 27 and 20 amino acids, respectively, from their amino termini. To explore the properties of the precursor-specific sequences, we exchanged the coding elements for these domains in the sigma(E) and sigma(K) structural genes and determined the properties of the resulting chimeric proteins in B. subtilis. The pro-sigma(E)-sigma(K) chimera accumulated and was cleaved into active sigma(K), while the pro-sigma(K)-sigma(E) fusion protein failed to accumulate and is likely unstable in B. subtilis. A fusion of the sigE ''pro'' sequence to an unrelated protein (bovine rhodanese) also formed a protein that was cleaved by the pro-sigma(E) processing apparatus. The data suggest that the sigma(E) pro sequence contains sufficient information for pro-sigma(E) processing as well as a unique quality needed for sigma(E) accumulation.