Expression of the Pneumocystis carinii major surface glycoprotein epitope is correlated with linkage of the cognate gene to the upstream conserved sequence locus

Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, Cincinnati, OH 45267, USA Correspondence James R. Stringer stringjr{at}ucmail.uc.edu The major surface glycoprotein (MSG) is a variable surface antigen of the pathogenic fungus Pneumocystis carinii . Many forms of MSG are encoded by a gene family. Expression of the MSG gene family is believed to be controlled in a cis -dependent fashion. Transcription of a given MSG gene is correlated with linkage of that gene to a unique locus called the upstream conserved sequence (UCS). These data predict that the MSG protein on a given organism will match that encoded by the MSG gene at the UCS locus in that organism. To test this hypothesis, a monoclonal antibody (mAb) that recognizes a small number of MSG isoforms was identified, and the DNA sequence encoding the mAb epitope (epitope-encoding sequence, EES) was determined. Western blotting, immunofluorescence and DNA hybridization showed that expression of the mAb epitope was associated with the presence of the EES at the UCS locus. Correlation of epitope expression and UCS linkage supports the hypothesis that expression of a particular MSG on the surface requires UCS linkage of the gene encoding it. Abbreviations: AP, alkaline phosphatase; ConA, concanavalin A; CRJE, conserved recombination junction element; DAPI, 4',6-diamidino-2-phenylindole; EES, epitope-encoding sequence; IFA, indirect immunofluorescence assay; MSG, major surface glycoprotein; TMAC, tetramethylammonium chloride; UCS, upstream conserved sequence The GenBank accession numbers for the MSG gene sequences determined in this work are: S5, AF164561 ; 60A9, AF169405 ; J3, AF169406 . Present address: House Staff Office, Cincinnati Children's Hospital Medical Center, 3333 Burnet Ave, Cincinnati, OH 45227, USA.