The
unc-6 gene encodes an unusual laminin B2 chain (~2.7 kb mRNA). The first 7 exons of the gene have been sequenced and the predicted protein is homologous to the N-terminal domains V and V1 of known laminin B chains (1). Domain V1 is globular and domain V consists of EGF-like repeats. Mutations in the
unc-6 gene affect dorsal and ventral cell migration guidance (2). The
unc-5 gene has been shown to act in combination with
unc-6 to affect dorsal cell migrations. The predicted protein product of the
unc-5 gene is a transmembrane receptor (3). Four
unc-6 alleles,
rh69,
rh202,
rh204, and
rh402, selectively disrupt dorsal cell migrations. We have examined these mutations in detail since they might define a domain of the laminin molecule involved with binding to the
unc-5 receptor. Restriction fragment polymorphisms were found in the DNA of strains with the
rh202,
rh204, or
rh402 allele. The polymorphisms were mapped and PCR was used to clone the DNA sequence. As shown below, the three alleles have deletions of the region containing the coding sequences for the second EGF-like repeat in domain V. The fourth allele,
rh69, was found to be a point mutation in a splice consensus sequence of the small intron within the V-2 coding sequence. We have not yet looked at the RNA splicing patterns in these strains, however we speculate that the exons for repeats V-1 and V-3 are spliced together, creating a slightly smaller protein lacking repeat V-2. [See Figure 1]