The PARP promoter of Trypanosoma brucei is developmentally regulated in a chromosomal context

African trypanosomes are extracellular protozoan parasites that are transmitted from one mammalian host to the next by tsetse flies, Bloodstream forms express variant surface glycoprotein (VSG); the tsetse fly (procyclic) forms express instead the procyclic acidic repetitive protein (PARP), PARP mRNA is abundant in procyclic forms and almost undetectable in bloodstream forms, post-transcriptional mechanisms are mainly responsible for PARP mRNA regulation but results of nuclear run-on experiments suggested that transcription might also be regulated. We measured the activity of genomically-integrated PARP, VSG and rRNA promoters in permanently-transformed bloodstream and procyclic form trypanosomes, using reporter gene constructs that showed no posttranscriptional regulation, When the constructs were integrated in the rRNA non-transcribed spacer, the ribosomal RNA and VSG promoters were not developmentally regulated, but integration at the PARP locus reduced rRNA promoter activity in bloodstream forms, PARR promoter activity was 5-fold down-regulated in bloodstream forms when integrated at either site, Regulation was probably at the level of transcriptional initiation, but elongation through plasmid vector sequences was also reduced.