We are studying the
nhr-1 (nuclear hormone receptor) gene, one of a number of steroid receptor homologues identified in C. elegans. Sequencing of the cDNA has shown interesting features for this putative "orphan" receptor, including an unusual sequence in the P box of the DNA binding domain, which might indicate a very different DNA binding specificity and function, and a very long 3' untranslated region. The
nhr-1 gene has been mapped to the right arm of the X chromosome, very close to
sup-10. We are now characterizing the genomic organization of
nhr-1 in C. elegans. We have also initiated work with C. briggsae in order to identify conserved, functionally important regions. The presence of an apparent homologue in C. briggsae was of special interest to us, given the unusual properties of
nhr-1 (different P box, the long 3'UT region), and the apparent viability of homozygous deficiencies in this region around
sup-10 (C. Cummins and P. Anderson). The C. elegans
nhr-1 gene appears to contain 12 exons spread over 9.5 kb, including several relatively large introns, 1.3 to 2.3 kb in size. Work to date with genomic clones from C. briggsae shows conserved exons which share approximately 81-84% homology at the nucleotide level with the
nhr-1 gene in C. elegans. This conservation between species, in the absence of a lethal phenotype for the homozygous deficiency, suggests that the
nhr-1 gene may nevertheless have an evolutionarily relevant function. We wish to thank Ann Sluder, Gary Ruvkun, Claudia Cummins and Dave Baillie et al. for their assistance, and Alan Coulson et al. for help with mapping clones. Supported by a Research Reorientation Associateship (NSERC Canada) to SS, and an NSERC Operating grant to BMH.