Analysis of post-transcriptional regulation operating on transcription products of the tandemly linked Leishmania infantum hsp70 genes.

The genomic organization and expression of the hsp70 genes of Leishmania infantum were examined. In the cluster there are at least six copies of the hsp70 genes arranged in a head-to-tail tandem of 3. 8-kilobase repetition units. The hsp70 gene copy (gene 6) located at the 3' end of the tandem has a 3'-untranslated region highly divergent in sequence relative to the 3'-untranslated region of the rest of hsp70 gene copies (genes 1-5). Nuclease S1 protection assays indicated that the steady-state level of the mRNAs derived from gene 6 is about 50-fold more abundant than the transcript level derived from genes 1-5. Nuclear run-on assays showed, however, that all hsp70 genes are transcribed at similar rates. Thus, it is likely that the differences in the steady-state levels of the transcripts from the hsp70 genes should be associated with variations in their processing or maturation rates. While the abundance of the mRNAs derived from hsp70 genes 1-5 is increased by heat shock, the hsp70 gene 6 mRNA level remains unaffected. Our data showed that ongoing protein synthesis is required for the maintenance of the heat inducement, depicting, thus, a post-transcriptional mechanism of positive regulation involving a labile protein factor that would be either induced or activated during heat shock.