An RNA polymerase II promoter in the hsp70 locus of Trypanosoma brucei

Abstract

To study of structure of RNA polymerase (pol) II transcription units a nd the influence of temperature on the regulation of gene expression in Trypanosoma brucei, and hsp70 intergenic region promoter was characterized. In T. brucei, the hsp70 locus contains, from 5' to 3', a cognate hsp70-related gene (gene 1) which is separated by about 6 kb of DNA from a cluster of five identical hsp70 genes (genes 2 to 6). Transcription proceeds on the entire 23-kb locus, and polycistronic transcription occurs in hsp70 genes 2 to 6. Transcription of hsp70 genes 2 to 6 is only moderately sensitive to UV irradiation, indicating that it cannot be driven by a single far-upstream promoter, which suggests that promoters could be located in the region close to the hsp70 coding region. Transient transformations demonstrated that sequences located upstream of hsp70 gene 2 and in the intergenic region between hsp70 genes 2 and 3 are able to direct transcription of the reporter gene, the chloramphenicol acetyltransferase (CAT) gene. The plasmid DNA driven by the hsp70 intergenic region promoter gave CAT activity approximately 85-fold above to background level. This is equivalent to approximately 1% of that derived from a CAT plasmid driven by the procyclic acidic repetitive protein gene promoter, which is controlled by RNA pol I. The hsp70 intergenic region promoter can drive alpha-amanitin-sensitive transcription at an internal position of the chromosome as well as an episome, suggesting that it is controlled by RNA pol II. However, this hsp70 intergenic region promoter, along with the 3' splice site and the 5' untranslated region of the hsp70 genes that controls the transcription of the reporter gene, cannot up-regulate the expression of the reporter gene during heat shock. This result is consistent with the previous observation that expression of the hsp70 genes in T. brucei is mainly controlled at the posttranscriptional level.