Different mutations in the
sqt-1 and
rol-6 collagen genes of Caenorhabditis elegans can cause diverse changes in body morphology and display different genetic attributes. We have determined the nucleotide alterations in 15 mutant alleles of these genes. Three mutations in
sqt-1 and one in
rol-6 that cause dominant right-handed helical twisting (RRol) of animals are arginine to cysteine replacements. These mutations are all within a short conserved sequence, on the amino terminal side of the Gly-X-Y repeats, that is found in all C. elegans cuticle collagens. A recessive RRol mutation of
rol-6 is a replacement of one of the same conserved arginines by histidine. In contrast, three
sqt-1 mutations that cause recessive left-handed helical twisting (LRol) are replacements of a conserved carboxy-terminal cysteine residue with either tyrosine or serine. These results suggest that disulfide bonding is important in collagen organization and that a deficit or surplus of disulfides may cause cuticle alterations of opposite handedness. In contrast to other collagens, glycine replacement mutations in the Gly-X-Y repeats of
sqt-1 cause very mild phenotypes. Nonsense mutations of both
sqt-1 and
rol-6 cause nearly, but not totally, wild-type phenotypes. A nonsense mutation in
sqt-1 suppresses the phenotype of
rol-6 RRol mutations, suggesting that
rol-6 collagen function is dependent on the presence of
sqt-1 collagen. Mutations of
sqt-1 are not suppressed by a
rol-6 nonsense mutation, however, indicating that
sqt-1 collagen can function independently of
rol-6.