THE PARP PROMOTER OF TRYPANOSOMA-BRUCEI IS DEVELOPMENTALLY-REGULATED IN A CHROMOSOMAL CONTEXT

African trypanosomes are extracellular protozoan parasites that are tr ansmitted from one mammalian host to the next by tsetse flies, Bloodst ream forms express variant surface glycoprotein (VSG); the tsetse fly (procyclic) forms express instead the procyclic acidic repetitive prot ein (PARP), PARP mRNA is abundant in procyclic forms and almost undete ctable in bloodstream forms, post-transcriptional mechanisms are mainl y responsible for PARP mRNA regulation but results of nuclear run-on e xperiments suggested that transcription might also be regulated. We me asured the activity of genomically-integrated PARP, VSG and rRNA promo ters in permanently-transformed bloodstream and procyclic form trypano somes, using reporter gene constructs that showed no posttranscription al regulation, When the constructs were integrated in the rRNA non-tra nscribed spacer, the ribosomal RNA and VSG promoters were not developm entally regulated, but integration at the PARP locus reduced rRNA prom oter activity in bloodstream forms, PARR promoter activity was 5-fold down-regulated in bloodstream forms when integrated at either site, Re gulation was probably at the level of transcriptional initiation, but elongation through plasmid vector sequences was also reduced.