The PrsA lipoprotein is essential for protein secretion in Bacillus subtilis and sets a limit for high-level secretion.

Mutations of the prsA gene of Bacillus subtilis have indicated that the gene is involved in protein secretion and it encodes a novel component of the cellular secretion machinery. We now demonstrate that the gene product is a membrane-associated lipoprotein, presumably bound to the outer face of the cytoplasmic membrane. Experiments to inactivate the prsA gene with insertions indicated that it is indispensable for viability. The cellular level of PrsA protein was shown to be decreased in prsA mutants with decreased level of exoproteins, consistent with an essential function in protein secretion. An increased amount of cellular PrsA protein was introduced by increasing the copy number of prsA in B. subtilis. This enhanced, from six- to twofold, the secretion of alpha-amylases and a protease in strains, which expressed high levels of these exoenzymes. This suggests that PrsA protein is the rate-limiting component of the secretion machinery, a finding that is of considerable biotechnological interest.