Nucleotide sequences responsible for the thermal inducibility of the Drosophila small heat-shock protein genes in monkey COS cells

Abstract

The promoter regions of the Drosophila melanogaster small heat-shock protein genes have been analysed in order to localize those sequences responsible for their heat-shock transcriptional inducibility. Different lengths of the 5′ DNA sequences of these four genes were each fused individually to the Herpes simplex virus thymidine kinase ( HSV-tk) transcription unit. These hybrid genes were constructed in a simian virus 40 recombinant vector for transfection in permissive monkey COS cells and tested for their heat-shock inducibility. The hsp22 HSV- tk and hsp26 HSV- tk fusion genes were found to be heat-inducible at 43 °C, giving rise to correctly initiated transcripts, but transcriptionally quiescent at 37 °C (control temperature). The hsp23 and hsp27 fusion gene constructs are, however, not heat-shock-inducible; no transcripts being detectable from hsp27 HSV- tk constructs at either temperature and all hsp23 HSV- tk clones being faithfully but constitutively expressed at low levels at both temperatures. By testing a series of 5′ deletion mutants in hsp22 HSV- tk , a homologous sequence located adjacent to the TATA box in both the hsp22 and hsp26 genes was identified as being responsible for their heat-shock activation. This control element corresponds to the Pelham “consensus sequence”, previously described for the Drosophila hsp70 genes. The possible modes of transcriptional induction of all four genes are discussed.