Heat-shock disruption of trans-splicing in trypanosomes: effect on Hsp70, Hsp85 and tubulin mRNA synthesis.

The synthesis of most, if not all, mRNA in trypanosomes involves the splicing in trans of two RNA molecules. One of these includes the common 5' mini-exon or spliced-leader sequence, while the other contains the complete protein-coding exon sequence for a given gene. We have recently shown that trans-splicing of tubulin transcripts is disrupted by heat shock, whereas trans-splicing of Hsp70 mRNA continues unabated, despite the increased expression of this latter gene [Muhich and Boothroyd, Mol. Cell Biol. 8 (1988) 3837-3846]. In this report we show that, in addition to being polyadenylated, the dimeric beta-alpha tubulin transcripts which accumulate as a result of heat shock have a correctly processed 5'-end (through mini-exon addition), and that the extent of disruption is proportional to the degree of heat shock. We further show that mRNA levels for two evolutionarily-conserved heat-shock proteins, Hsp70 and Hsp85, are increased under the splicing-disruptive conditions of heat shock.