A Tandem Repeat of Rat‐derived Pneumocystis carinii Genes Encoding the Major Surface Glycoprotein

Abstract

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.

Adoptive transfer of lymphocytes sensitized to the major surface glycoprotein of Pneumocystis carinii confers protection in the rat.

“…Gigliotti et al (18), using immunoelectron microscopy, demonstrated that MSG is distributed on the surface of all developmental stages of P. carinji. Through molecular studies of rat and ferret P. carindi, it has been demonstrated that MSG represents a group of proteins encoded by multiple genes (6)(7)(8)19). Numerous unique MSG cDNAs have been identified, establishing that multiple mRNAs are transcribed within a population of organisms (6)(7)(8)(9).…”

“…With the recent progress in cloning and expressing MSG genes (6)(7)(8)(9), it should be possible to develop T cell clones, map their epitopes, and test their functional importance in vivo.…”

“…MSG, which actually represents a family of related proteins encoded by unique genes (6)(7)(8)(9), is highly immunogenic and elicits both humoral and cellular immune responses (10)(11)(12)(13)(14). It has been demonstrated that MSG is a specific T cell antigen and significantly increases the percentage of CD4 + T cells during the proliferative response (14).…”

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

“…A P. carinii genomic library was constructed in lgt11 by standard methods (Sambrook et al, 1989;Linke et al, 1998). Approximately 3x10 6 plaques were screened with the RA-C11 mAb, and positive plaques were isolated as described previously (Sunkin et al, 1994;Garbe & Stringer 1994;Schaffzin, 1999). For analysis of proteins encoded by a lgt11 clone, crude lysates were generated from bacteria (Escherichia coli Y1090r 2 ) lysogenic for the phage (Sambrook et al, 1989).…”

“…carinii organisms express a surface antigen known as the major surface glycoprotein (MSG) (Walzer & Linke, 1987;Kovacs et al, 1988;Tanabe et al, 1989;Nakamura, 1998;. Multiple forms of MSG are encoded by a family of approximately 100 genes, members of which are located at 34 telomeric sites (Stringer et al, 1991;Kovacs et al, 1993;Sunkin et al, 1994;Sunkin & Stringer, 1996, 1997Cornillot et al, 2002;Keely et al, 2003). Other species of Pneumocystis, including the species that infects humans, also have families of MSG genes (Haidaris et al, 1991;Stringer et al, 1993;Garbe & Stringer, 1994;Wright et al, 1995;Mei et al, 1998;Haidaris et al, 1998;Schaffzin et al, 1999;Kutty et al, 2001).…”