Membrane phospholipid synthesis in Escherichia coli. Identification of the sn-glycerol-3-phosphate acyltransferase polypeptide as the plsB gene product

Abstract

A collection of hybrid plasmids bearing a structural gene, plsB, for the sn-glycerol-3-phosphate acyltransferase of Escherichia cole (Lightner, V. A., Larson, T. J., Tailleur, P., Kantor, G. D., Raetz, C. R. H., Bell, R. M., and Modrich, P. (1980) J. Biol. Chem. 255, 9413-9420) was employed to identify the membrane protein which is the sn-glycerol-3-phosphate acyltransferase. Strains containing these hybrid plasmids exhibited a marked increase in sn-glycerol-3-phosphate acyltransferase activity which was quantitatively extracted from membrane preparations with Triton X-100. Analysis of polypeptides present in detergent extracts of membranes from strains harboring the hybrid plasmids revealed a marked overproduction of a protein with an apparent molecular weight of 83,000, which was also the major protein labeled in minicells containing these hybrid plasmids. The labeled 83,000-dalton protein cochromatographed with sn-glycerol-3-phosphate acyltransferase activity on DEAE-cellulose. Utilization of three hybrid plasmids bearing amber mutations within the plsB gene demonstrated that the 83,000-dalton protein is the sn-glycerol-3-phosphate acyltransferase. Analysis of Bam HI deletion plasmids demonstrated that a 2.3-megadalton DNA fragment is necessary and sufficient for expression of the plsB gene. The sn-glycerol-3-phosphate acyltransferase was purified to near homogeneity from Triton X-100 extracts of membranes from overproducing strains. The preparations had reconstitutable specific activity of 2.5 micromol/min/mg and contained a single polypeptide with an apparent molecular weight of 83,000.