Characterization of the hsp70 multigene family of Caenorhabditis elegans.

Our laboratory has been characterizing the hsp70 multigene family from the nematode Caenorhabditis elegans as the first step to the genetic characterization of the heat shock response in a relatively simple multicellular eukaryote. Two gene members, hsp-1 and hsp-2ps have already been characterized (Snutch et al., 1988; Heschl and Baillie, 1989). The third gene member, hsp-3, is expressed constitutively and is non-heat inducible; its mRNA is most abundant at the L1 larval stage. The hsp-3 protein (hsp70C) shares a high degree of identity with the rat grp78 protein and has a long, hydrophobic leader sequence. The carboxyl terminus of hsp70C has the putative ER-retention signal, KDEL. The fourth gene member, hsp-6 is expressed constitutively and moderately heat inducible. A partial hsp-6 protein (hsp70F) sequence shares a higher degree of identity with the Escherichia coli dnaK protein than with eukaryotic hsp70 proteins. The predicted amino-terminal half of the hsp70F polypeptide also contains a long, amphiphilic leader sequence similar to mitochondrial import leader sequences. These two genes encode proteins that potentially cross intracellular membranes. We compared the 5'-flanking DNA from the C. elegans hsp-3 gene to fragment containing enhancer activity from the rat grp78 gene regulatory region (Lin et al., 1986). A 23-nucleotide sequence was conserved between the two promoter regions. This sequence shares approximately 80% identity between these two evolutionary distant organisms. A comparison to other hsp70 genes did not reveal any conservation of this 23-nucleotide sequence. We propose that this sequence may be involved in a unique aspect of the regulation of the C. elegans' grp78-like gene and the rat grp78 gene.