EXPRESSION OF HEAT-SHOCK PROTEIN-83 IN LEISHMANIA IS REGULATED POSTTRANSCRIPTIONALLY

Mechanisms for regulation of heat shock protein (hsp) 83 expression we re examined in Leishmania amazonensis. Transcripts of hsp83 accumulate d upon temperature elevation; however, in contrast to non-protozoan eu karyotes (i.e. Drosophila, yeast, avian or human cells), no transcript ional activation was observed. The increase in the hsp83 mRNA level ev olved from temperature induced variations in mRNA turn-over: the hsp83 transcript was rapidly degraded at normal temperatures, whereas heat shock led to its stabilization. The quick decay of the mRNA at lower t emperatures was dependent on active protein synthesis. A similar patte rn of regulation was observed for the transfected chloramphenicol acet yltransferase (CAT) gene, which was flanked by sequences from the hsp8 3 intergenic region (IR), and cloned into the pX transfection vector ( pX-ICI). CAT mRNA was abundant at normal temperatures and further accu mulated upon temperature elevation. The altered turn-over rates of CAT mRNA at the different temperatures were observed only in the presence of flanking hsp83 IR sequences. The increase in temperature also affe cted translational regulation of hsps, and synthesis of hsp83 was more efficient at 35 degrees C than at 26 degrees C. However, the effect o n translation was transient, and the steady state level of the protein was hardly altered.