POSTTRANSCRIPTIONAL CONTROL OF HSP70 MESSENGER-RNA IN TRYPANOSOMA-BRUCEI

The control of hsp70 mRNA levels was investigated using transgenic blo odstream and procyclic trypanosomes. Heat shock of procyclic and blood stream trypanosomes caused no significant change in overall protein sy nthesis, but led to a 2-3-fold increase in the relative hsp70 mRNA lev el in bloodstream trypanosomes. Incubation of procyclic trypanosomes a t 35 degrees C for up to 18 h increased the level of hsp70 mRNA only m arginally. The expression of actin and hsp70 mRNAs was markedly reduce d in late log phase procyclic trypanosomes but PARP mRNA levels remain ed constant. Measurements of phleomycin-binding-protein RNAs bearing 3 '- and 5'-untranslated regions from the actin, PARP or hsp70 loci indi cated that both the heat-shock and cell-density effects were mediated by the untranslated regions, No significant promoter activity was dete cted in the different hsp70 locus intergenic regions in transient assa ys.