ANALYSIS OF POSTTRANSCRIPTIONAL REGULATION OPERATING ON TRANSCRIPTIONPRODUCTS OF THE TANDEMLY LINKED LEISHMANIA-INFANTUM HSP70 GENES

The genomic organization and expression of the hsp70 genes of Leishman ia infantum were examined. In the cluster there are at least six copie s 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 sequenc e relative to the 3'-untranslated region of the rest of hsp70 gene cop ies (genes 1-5). Nuclease S1 protection assays indicated that the stea dy-state level of the mRNAs derived from gene 6 is about SO-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 si milar rates. Thus, it is likely that the differences in the steady-sta te levels of the transcripts from the hsp70 genes should be associated with variations in their processing or maturation rates. While the ab undance of the mRNAs derived from hsp70 genes 1-5 is increased by heat shock, the hsp70 gene 6 mRNA level remains unaffected. Our data showe d that ongoing protein synthesis is required for the maintenance of th e heat inducement, depicting, thus, a post-transcriptional mechanism o f positive regulation involving a labile protein factor that would be either induced or activated during heat shock.