We describe the molecular analysis of the
dpy-20 gene in Caenorhabditis elegans. Isolation of genomic sequences was facilitated by the availability of a mutation that resulted from insertion of a Tcl transposable element into the
dpy-20 gene. The Tcl insertion site in the
m474::Tcl allele was identified and was found to lie within the coding region of
dpy-20. Three revertants (two wild-type and one partial revertant) resulted from the excision of this Tcl element. Genomic
dpy-20 clones were isolated from a library of wild-type DNA and were found to lie just to the left of the
unc-22 locus on the physical map, compatible with the position of
dpy-20 on the genetic map. Cosmid DNA containing the
dpy-20 gene was successfully used to rescue the mutant phenotype of animals homozygous for another
dpy-20 allele,
e1282ts. Sequence analysis of the putative
dpy-20 homologue in Caenorhabditis briggsae was performed to confirm identification of the coding regions of the C. elegans gene and to identify conserved regulatory regions. Sequence analysis of
dpy-20 revealed that it was not similar to other genes encoding known cuticle components such as collagen or cuticulin. The
dpy-20 gene product, therefore, identifies a previously unknown type of protein that may be directly or indirectly involved in cuticle function. Northern blot analysis showed that
dpy-20 is expressed predominantly in the second larval stage and that the mRNA is not at all abundant. Data from temperature shift studies using the temperature-sensitive allele
e1282ts showed that the sensitive period also occurs at approximately the second larval stage. Therefore, expression of
dpy-20 mRNA and function of the DPY-20 protein are closely linked temporally.