UNC-68 ENCODES A RYANODINE RECEPTOR INVOLVED IN REGULATING C-ELEGANS BODY-WALL MUSCLE-CONTRACTION

Striated muscle contraction is elicited by the release of stored calci um ions through ryanodine receptor channels in the sarcoplasmic reticu lum. ryr-1 is a C. elegans ryanodine receptor homologue that is expres sed in body-wall muscle cells used for locomotion. Using genetic metho ds, we show that ryr-1 is the previously identified locus unc-68. Firs t, transposon-induced deletions within ryr-1 are alleles of unc-68. Se cond, transformation of unc-68 mutants with ryr-1 genomic DNA results in rescue of the Unc phenotype. unc-68 mutants move poorly, exhibiting an incomplete flaccid paralysis, yet have normal muscle ultrastructur e. The mutants are insensitive to the paralytic effects of ryanodine, and lack detectable ryanodine-binding activity. The Unc-68 phenotype s uggests that ryanodine receptors are not essential for excitation-cont raction coupling in nematodes, but act to amplify a (calcium) signal t hat is sufficient for contraction.