cDNA sequence diversity and genomic clusters of major surface glycoprotein genes of Pneumocystis carinii

A tandem repeat of rat-derived Pneumocystis carinii genes encoding the major surface glycoprotein

A fragment from the genome of rat-derived Pneumocystis carinii was found to contain two MSG genes arranged as a direct repeat. The sequences from one gene (MSG B), the region between the two genes, and part of the second gene (MSG A) were determined. The two MSG genes were not identical in sequence. The open reading frames of MSG A and MSG B encode non-identical proteins, both of which are similar to that encoded by a previously published cDNA. The MSG B gene sequence showed no evidence of introns. The 5' and 3' untranslated regions of the MSG gene pair were highly conserved, but the regions immediately upstream of the open reading frames of MSG A and B were different from the region upstream of a previously characterized MSG cDNA. Primers designed to extend upstream of the 5' end of MSG and downstream of the 3' end of MSG were used in a polymerase chain reaction with total genomic P. carinii DNA as template. Presumptive intergenic amplification products from this reaction were cloned and sequenced. The sequences of these regions were similar but distinct, indicating that tandem arrangement of MSG genes is a common organizational motif.

Characterization of multiple unique cDNAs encoding the major surface glycoprotein of rat-derived Pneumocystis carinii

The major surface glycoprotein (MSG) of rat-derived Pneumocystis carinii represents a group of related molecules that are encoded by multiple genes. We isolated seven unique MSG cDNAs from a library prepared from a single infected rat lung. The cDNAs displayed both conserved and variant regions to previously described cDNAs. These clones contained inserts that ranged in size from 0.4 to 1.8 kb and all contained a poly(A) tail. The largest clone, Pc1410, hybridized to all 15 chromosomes resolved by pulsed-field gel electrophoresis (PFGE). Protein produced by in vitro translation from Pc1410 was immunoprecipitated with affinity-purified MSG antibodies. The clones were characterized by DNA sequencing of their 3' and 5' ends. Analysis of the untranslated and coding regions demonstrated that the clones contained unique and conserved regions of sequence, but none of the clones were identical. Isolation of seven additional unique clones picked from a single screening of a cDNA library suggests that numerous MSG transcripts exist within a population of P. carinii.