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Pseudomonas aeruginosa Synthesizes Phosphatidylcholine by Use of the Phosphatidylcholine Synthase Pathway. Paula J. Wilderman, 2002.Phosphatidylcholine (PC) is a ubiquitous membrane lipid in eukaryotes but has been found in only a limited number of prokaryotes . Both eukaryotes and prokaryotes synthesize PC by methylating phosphatidylethanolamine (PE) by use of a phospholipid methyltransferase (Pmt) . Eukaryotes can synthesize PC by the activation of choline to form choline phosphate and then CDP-choline . The CDP-choline then condenses with diacylglycerol (DAG) to form PC . In contrast, prokaryotes condense choline directly with CDP-DAG by use of the enzyme PC synthase (Pcs) . PmtA was the first enzyme identified in prokaryotes that catalyzes the synthesis of PC, and Pcs in Sinorhizobium meliloti was characterized . The completed release of the Pseudomonas aeruginosa PAO1 genomic sequence contains on open reading frame predicted to encode a protein that is highly homologous (35% identity, 54% similarity) to PmtA from Rhodobacter sphaeroides . Moreover, the P . aeruginosa PAO1 genome encodes a protein with significant homology (39% amino acid identity) to Pcs of S . meliloti . Both the pcs and pmtA homologues were cloned from PAO1, and homologous sequences were found in almost all of the P . aeruginosa strains examined . Although the pathway for synthesizing PC by use of Pcs is functional in P . aeruginosa, it does not appear that this organism uses the PmtA pathway for PC synthesis . We demonstrate that the PC synthesized by P . aeruginosa PAO1 localized to both the inner and outer membranes, where it is readily accessible to its periplasmic, PC-specific phospholipase D . Role of RopB in Growth Phase Expression of the SpeB Cysteine Protease of Streptococcus pyogenes. Melody N. Neely, 2003.The Rgg family of transcription regulators is widely distributed among gram-positive bacteria; however, how the members of this family control transcription is poorly understood . In the pathogen Streptococcus pyogenes, the Rgg family member RopB is required for transcription of the gene that encodes the secreted SpeB cysteine protease . Expression of the protease follows distinct kinetics that involves control of transcription in response to the growth phase . In this study, the contribution of RopB to growth phase control was examined . The gene encoding the protease (speB) and ropB are transcribed divergently from a 940-bp intergenic region . Primer extension analyses, in conjunction with reporter fusion studies, revealed that the major region controlling the transcription of both speB and ropB is adjacent to ropB and that the promoters for the two genes likely overlap . Furthermore, it was found that RopB is a DNA-binding protein that specifically binds to sequences in this control region . The interrelationship between ropB and speB expression was further reflected in the observation that transcription of ropB itself is subject to growth phase control . However, while expression of ropB from a promoter expressed during the early logarithmic phase of growth could complement a ropB deletion mutant, ectopic expression of ropB did not uncouple the expression of speB from its growth phase signal . These data implicate other factors in growth phase control and suggest that regulation of ropB expression itself is not the central mechanism of control .
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