Zinc-metalloproteases of the BMP-1/TOLLOID family are involved in various developmental processes, such as embryonic patterning, extracellular matrix formation, remodelling, and degradation. In particular, mammalian BMP-1 acts as convertase for several collagen precursors. The C. elegans genome contains 40 genes coding for BMP-1 homologues; two such genes have been characterised and are required for hatching and moulting, respectively. We have studied a third member of this family, which was named
dpy-31 after its Dpy mutant phenotype. Mutations in this gene cause defective cuticle structure and embryonic lethality, indicating that
dpy-31 is essential for synthesis of the nematode cuticle. We conducted mutagenesis screens for suppressors of
dpy-31 and found that the lethality associated with
dpy-31 can be rescued by one mutation in the collagen gene
dpy-17 and by multiple mutations in the uniquely essential collagen gene
sqt-3. While the effect of the mutation in
dpy-17 is enigmatic, the numerous suppressor mutations in
sqt-3 point to a plausible model for interaction between DPY-31 and SQT-3. The suppressor strains carry 11 distinct missense mutations altering 8 conserved amino acid residues in the SQT-3 C-terminus. The genetic properties of the suppressors indicate that DPY-31 is likely to be responsible for processing of the SQT-3 C-terminus and that the mutations can bypass the requirement for cleavage by DPY-31. IFA using a SQT-3-specific serum show that SQT-3 fails to localise correctly in a
dpy-31 mutant background, supporting the hypothesis that DPY-31 is required for SQT-3 assembly. Taken together, our data suggest that involvement of proteases of the BMP-1/TOLLOID family in proteolytic maturation of collagen trimers is conserved between mammals and nematodes. In addition, we characterised molecularly a novel informational suppressor,
sup-32.
sup-32 acts in an allele-specific, gene-unspecific fashion to weakly suppress amber stop codons. Unlike most other amber suppressors, which are tRNATrp,
sup-32 is a tRNAGln. A single base substitution in a tRNAGln was identified in independent
sup-32 isolates which converts a tRNAGln minority codon (CAG) into an amber codon (UAG). This is the first report of a tRNAGln amber suppressor in metazoans.