No abstract

Pneumocystis carinii is an opportunistic agent found in the lung of various mammals which often causes severe pneumonia in immunocompromised humans, especially in AIDS patients. In the past several years significant additions have been made to the collection of knowledge we have concerning the genetic diversity of P. carinii. These additions provide new understanding of Pneumocystis transmission and the effect of possible reservoirs of Pneumocystis in the various species. In this study, a 400-bp fragment of the thymidylate synthase (TS) gene of P. carinii has been amplified by PCR from 43 parasite isolates obtained from 4 mammalian host species: rat, mouse, rabbit and human. A probe selected from the TS gene sequence of rat-derived P. carinii was hybridized with the amplified products from rat- and mouse-derived P. carinii, but not with rabbit or human P. carinii DNA. Restriction profiles were performed on amplified fragments from all isolates, and the 4 nucleotide sequences of the TS gene fragment amplified from rat, mouse, rabbit and human P. carinii were determined. Differences were detected in the gene fragment in P. carinii isolates from the 4 host species; however no difference was revealed in P. carinii isolates within a single host species, whatever the host strain or its geographic origin. Thus, the sequence differences of the P. carinii TS gene appeared as host-species specific. A specific probe which recognized all human P. carinii isolates was defined.

No abstract

Osmoregulated periplasmic glucans (OPGs) of Escherichia coli are anionic and highly branched oligosaccharides that accumulate in the periplasmic space in response to low osmolarity of the medium. The glucan length, ranging from 5 to 12 glucose residues, is under strict control. Two genes that form an operon, mdoGH, govern glucose backbone synthesis. The new gene mdoD, which appears to be a paralog of mdoG, was characterized in this study. Cassette inactivation of mdoD resulted in production of OPGs with a higher degree of polymerization, indicating that OpgD, the mdoD product (according to the new nomenclature), controls the glucose backbone structures. OpgD secretion depends on the Tat secretory pathway. Orthologs of the mdoG and mdoD genes are found in various proteobacteria. Most of the OpgD orthologs exhibit a Tat-dependent secretion signal, while most of the OpgG orthologs are Sec dependent.Osmoregulated periplasmic glucans (OPGs) are a family of oligosaccharides found in the periplasm of gram-negative bacteria. Their common features are the presence of glucose as the sole constituent sugar and their increased levels in lowosmolarity media. These glucans are cyclic, branched cyclic, or branched linear, and they may be substituted by various residues in different species (3).In Escherichia coli, OPGs are composed of 5 to 12 glucose units, and the principal species contain eight or nine glucose residues. Despite this length heterogeneity, the distribution of the various glucose backbones is strictly conserved. The structure is highly branched, and the backbone consists of linear ␤-1,2-linked glucose units to which the branches are attached by ␤-1,6 linkages; the average number of branches is three. The glucose backbone is substituted with sn-1-phosphoglycerol and phosphoethanolamine, both derived from membrane phospholipids, and with succinic acid O-ester residues from the cytoplasmic pool (15, 18).OPGs were discovered by E. P. Kennedy and his collaborators during analysis of phosphatidylglycerol turnover in E. coli (31). sn-1-Phosphoglycerol was recovered on oligosaccharides named, for this reason, membrane-derived oligosaccharides.

No abstract

No abstract

This work reports the isolation and characterization of a gene encoding a superoxide dismutase (SOD, EC.1.15.1.1.) from Pneumocystis carinii derived from rat. Sense and antisense oligonucleotides, deduced from SOD amino acid sequences from a wide variety of organisms, allowed amplification of a 669 bp genomic DNA fragment specific to this P. carinii. RACE-PCR was used to obtain the major part of the complementary DNA; the 5'- and 3'-genomic regions were obtained respectively from a Mbol subgenomic library and from an amplified fragment using oligonucleotides designed from the cDNA sequence. Comparison of genomic and cDNA sequences showed an open reading frame of 660 bp interrupted by seven small introns. The deduced amino acid sequence contained 220 residues. Protein sequence alignment demonstrated the highest homology (50.5% identity; 70.3% similarity) with Saccharomyces cerevisiae manganese-SOD (MnSOD) suggesting that P. carinii SOD belongs to the mitochondrial MnSOD group. A putative targeting peptide found at the 5'-end of the P. carinii SOD sequence also suggested its mitochondrial localization.

No abstract