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 th e gene is involved in protein secretion and it encodes a novel compone nt of the cellular secretion machinery. We now demonstrate that the ge ne product is a membrane-associated lipoprotein, presumably bound to t he outer face of the cytoplasmic membrane. Experiments to inactivate t he prsA gene with insertions indicated that it is indispensable for vi ability. The cellular level of PrsA protein was shown to be decreased in prsA mutants with decreased level of exoproteins, consistent with a n essential function in protein secretion. An increased amount of cell ular 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-limi ting component of the secretion machinery, a finding that is of consid erable biotechnological interest.