The small heat shock genes of C. elegans encode a family of 16 kDa polypeptides which are strictly stress-inducible. Four distinct
hsp16 genes reside at two loci in the nematode genome. One region (hspl6A) contains genes hspl6-1 and
hsp16-48 while the other (
hsp16B) contains
hsp16-2 and
hsp16-41. At each locus the genes are arranged in opposite orientations, separated by approximately 350 bp. Transgenic animals were constructed carrying the hsp 16-48/1 intergenic region fused to lacZwith the
hsp16-48 promoter proximal to the reporter gene. When the animals were heat shocked and stained for ,B-gal activity, intense and extensive expression was observed in muscle and hypodermis with limited staining in the intestine and pharynx. When the
hsp16-1 promoter was proximal to lacZ, intense expression was seen in the intestine and nerve ganglia while expression in muscle and hypodermis was weaker and less consistent. A translational fusion of lacZ in- frame with the second exon of the whole hsp 16-1 gene provided the most generalized pattern of expression, encompassing intestine, muscle, hypodermis, pharynx and neNe, the latter appearing to be more extensive than for either of the two other constructs. A transcriptional fusion containing a fragment of the
hsp16-48/1 intergenic region which eliminated the HSEs and TATA box of
hsp16-1 but maintained a central stretch of alternating purines and pyrimidines provided strong embryonic expression, but somatic expression in other stages was weak and sporadic, limited usually only to muscle. Thus the deleted region must contain sequences required for postembryonic expression but unnecessary for embryonic expression. Transgenic animals containing the hsp 16-41/2 intergenic region with the
hsp16-41 promoter proximal to lacZ stained very intensely in the pharynx, the pharyngeal-intestinal valve, intestine and nervous tissue. Body muscle expression was infrequent and usually limited to the head whereas expression in pharyngeal muscle was very intense. Worms containing a lacZ fusion which eliminated the HSEs and TATA box of the
hsp16-2 gene but maintained the
hsp16-41 promoter expressed -gal in the intestine and less frequently in the vulva_ Embryos containing this construct stained strongly. No -gal activity was detected in any of these strains under non-shock conditions. These results suggest that there are inter-locus as well as intra-locus differences in the tissue-specific pattern of expression of the
hsp16 gene family. Supported by M. R. C. of Canada and the B.C. Health Research Foundation.