Monitoring Editor: Thomas Pollard Mutations in
unc-96 or
unc-98 cause reduced motility and a characteristic defect in muscle structure: by polarized light microscopy birefringent needles are found at the ends of muscle cells. Anti-paramyosin stains the needles in
unc-96 and
unc-98 mutant muscle. However there is no difference in the overall level of paramyosin in wild-type,
unc-96 and
unc-98 animals. Anti-UNC-98 and anti-paramyosin colocalize in the paramyosin accumulations of missense alleles of
unc-15 (encodes paramyosin). Anti-UNC-96 (Mercer et al., 2006) and anti-UNC-98 have diffuse localization within muscles of
unc-15 null mutants. By immunoblot, in the absence of paramyosin, UNC-98 is diminished, whereas in paramysoin missense mutants, UNC-98 is increased.
unc-98 and
unc-15, or
unc-96 and
unc-15 (Mercer et al., 2006) interact genetically either as double heterozygotes or as double homozygotes. By yeast 2-hybrid and ELISAs using purified proteins, UNC-98 interacts with paramyosin residues 31-693, whereas UNC-96 interacts with a separate region of paramyosin, residues 699-798. The importance of surface charge of this 99 residue region for UNC-96 binding was shown. Paramyosin lacking the C terminal UNC-96 binding region fails to localize throughout A-bands. We propose a model in which UNC-98 and UNC-96 may act as chaperones to promote the incorporation of paramyosin into thick filaments.