Enrichment of the bacteriophage PR4 membrane in phosphatidylglycerol is not essential for phage assembly and infectivity.

The membrane phospholipids of bacteriophage PR4 grown on wild-type Escherichia coli are markedly enriched in phosphatidylglycerol (PG) relative to host phospholipids. To investigate the role of PG in phage assembly and infectivity, we propagated PR4 on an E. coli mutant defective in PG synthesis. The PG content of PR4 grown on the mutant host accounted for 0.4% of the total viral phospholipids, representing a 90-fold decrease in PG relative to the PG content of phage grown on a wild-type host. Phosphatidylethanolamine and phosphatidic acid, the two major phospholipid species present in these phage preparations, accounted for 88.4 and 9.4% of the total viral phospholipids, respectively. This drastic alteration of the phage phospholipid composition had little or no adverse effect on either the stability or infectivity of the phage. We conclude that the enrichment of the PR4 virion in PG does not reflect an absolute structural requirement of the phage and is not essential for phage infectivity.     

Genetic characterization of the Escherichia coli cyclopropane fatty acid (cfa) locus and neighboring loci

Summary The phenotypically silent cyclopropane fatty acid synthesis (cfa) gene of Escherichia coli K-12 has been located on the genetic linkage map. This was accomplished by integrating (via homologous recombination) the selectable marker of a recombinant plasmid into the host chromosome near the cfa locus. This integration allowed the subsequent isolation of a cfa-linked transposon Tn10 insertion. Genetic mapping of the Tn10 insertion, using conventional techniques, placed the cfa locus at min 36.5 on the linkage map in the vicinity of several other non-selectable markers. We ordered cfa and these other loci by three-factor transductional analyses. Selection for excision of the Tn10 element resulted in several types of mutants which harbor mutations of cfa and of neighboring genes, presumably as a consequence of Tn10-catalyzed chromosomal rearrangements.     

The positional distribution of fatty acids in Escherichia coli phospholipids is not regulated by sn-glycerol 3-phosphate levels.

Large changes in the intracellular concentration of sn-glycerol 3-phosphate had no effect on the acyl chain distribution of the phospholipids of Escherichia coli. This result directly contradicts the prediction by other workers based on in vitro experiments.     

The putative fabJ gene of Escherichia coli fatty acid synthesis is the fabF gene.

Siggaard-Andersen and coworkers (M. Siggaard-Andersen, M. Wissenbach, J. Chuck, I. Svendsen, J. G. Olsen, and P. von Wettstein-Knowles, Proc. Natl. Acad. Sci. USA 91:11027-11031, 1994) recently reported the DNA sequence of a gene encoding a beta-ketoacyl-acyl carrier protein synthase from Escherichia coli. These workers assigned this gene the designation fabJ and reported that the gene encoded a new beta-ketoacyl-acyl carrier protein synthase. We report that the fabJ gene is the previously reported fabF gene that encodes the known beta-ketoacyl-acyl carrier protein synthase II.     

Further mapping of several membrane lipid biosynthetic genes (fabC, fabB, gpsA, plsB) of Escherichia coli.

New genetic mapping data on several loci involved in membrane lipid synthesis are reported. We demonstrated that the lesion designated fabC by Broekman and Hoeckstra (Mol. Gen. Genet. 124:65-67, 1975) is a fabB mutation. In the course of this work, the orientation of the pdxB and fabB loci was determined. The order of the loci is fabB pdxB purF. We also report cotransduction between the gpsA and cysE loci and show that the order of these markers is mtl cysE gpsA. Cotransduction between the plsB and kdgK loci was also sought. Despite extensive experiments, we were unable to detect cotransduction between these loci. In addition, we were unable to detect cotransduction among several markers in region 46 to 48 min of the map.