The PLB2 gene of Saccharomyces cerevisiae confers resistance to lysophosphatidylcholine and encodes a phospholipase B Lysophospholipase

The PLB1 gene of Saccharomyces cerevisiae encodes a protein that demonstrat es phospholipase B, lysophospholipase, and transacylase activities. Several genes with significant homology to PLB1 exist in the S. cerevisiae genome, raising the possibility that other proteins may contribute to the total ph ospholipase B/lysophospholipase/transacylase activities of the cell. We rep ort the isolation of a previously uncharacterized gene that is highly homol ogous to PLB1 and that, when overexpressed, confers resistance to 1-palmito yllysophosphatidylcholine. This gene, which is located adjacent to the PLB1 gene on the left arm of chromosome XIII and which we refer to as PLB2, enc odes a phospholipase B/lysophospholipase. Unlike PLB1, this gene product do es not contain significant transacylase activity. The PLB2 gene product sho ws lysophospholipase activity toward lysophosphatidylcholine, lysophosphati dylserine, and lysophosphatidylethanolamine. Whereas deletion of either PLB 1 or PLB2 resulted in the loss of 80% of cellular lysophospholipase activit y, a plb1/plb2 double deletion mutant is completely devoid of lysophospholi pase activity toward the preferred substrate lysophosphatidylcholine. Overe xpression of PLB2 was associated with an increase in total cellular phospho lipase B/lysophospholipase activity, as well as the appearance of significa nt lysophospholipase activity in the medium. Moreover, overexpression of PL B2 was associated with saturation at a higher cell density, and an increase in total cellular phospholipid content, but no change in phospholipid comp osition or fatty acid incorporation into cellular lipids. Deletion of PLB2 was not lethal and did not result in alteration of membrane phospholipid co mposition or content. PLB2 gene expression was found to be maximal during e xponential growth conditions and was decreased in late phase, in a manner s imilar to other genes involved in phospholipid metabolism.