Identification of a putative regulatory element in the 3'-untranslated region that controls expression of HSP70 in Leishmania infantum.

The regulation of HSP70 gene expression in Leishmania infantum, in contrast to most eukaryotes, occurs by mechanisms that operate exclusively at the post-transcriptional level. During the normal growth of L. infantum promastigotes at 26 degrees C the mRNAs derived from the sixth gene of the HSP70 locus are more abundant than the mRNAs derived from the other five HSP70 genes, but only the latter transcripts accumulate after incubation at 37 degrees C. Here, it was found that the full-length 3'untranslated region (UTR) and downstream sequences of the HSP70 genes are necessary for a correct polyadenylation of both types of transcripts and responsible for the differences in the steady-state levels of the transcripts. Also, it was found that the addition of the 3'-UTR-I (common to the first five genes of the L. infantum HSP70 gene cluster) to a reporter gene is sufficient to achieve an accumulation of the corresponding transcripts at 37 degrees C. This effect was, furthermore, found to be strand dependent. A progressive shortening of the 1063-base 3'-UTR-I has shown that the temperature-dependent accumulation was lost after deletion of 364-nucleotides from the 3' end. In addition, the accumulation of reporter transcripts at 37 degrees C was not observed in a plasmid construct containing an internal deletion (region 699-816) of the 3'-UTR-I. Thus, our data suggest that RNAs derived from L. infantum HSP70 genes 1-5 contain a cis-acting sequence that functions as a positive element during heat shock.