Elevated phosphoglycerate kinase mRNA but not protein in monomorphic Trypanosoma brucei: implications for stage-regulation and post-transcriptional control.

Phosphoglycerate kinase (PGK) is present in high levels in the glycosomes of bloodstream stage Trypanosoma brucei, but is virtually absent in procyclic stage glycosomes. Glycosomes isolated from slender and stumpy stage bloodforms show similar levels of PGK, although levels are slightly lower in stumpy forms. Lower levels of glycosomal PGK transcripts are observed in stumpy form RNA, paralleling the decrease in glycosomal PGK activity. Monomorphic strains and pleiomorphic strains show similar glycosomal PGK activity, but monomorphic strains have much higher levels of the glycosomal PGK transcript. In three separate cases, predominantly monomorphic strains derived from highly pleiomorphic strains showed increased levels of glycosomal PGK (gPGK) mRNA. gPGK synthesis rates in monomorphic and pleiomorphic strains were similar, and no significant differences in turnover were observed. These data suggest the possibility of translational control of gPGK protein levels in trypanosome bloodforms. The data also indicate that the metabolism of gPGK mRNA in highly passaged laboratory strains is altered, and counsel caution when attributing differences in transcript levels to stage-specific regulation.