The strain R73 has previously been described as a revertant of unc- 54
(e569) (Epstein, et al., J. Mol. Biol. (1974) 90:291-300; Mackenzie and Epstein, Nematode workshop, 1977). However, the fine structure as described by Mackenzie in Woods Hole strongly resembled the muscle of putative missense alleles of
unc-15 (Waterston, et al., J. Mol. Biol. in press) and not that of any of the other mutants so far isolated and examined (Waterston, unpublished). Accordingly, R73 was obtained from H. Epstein and further genetic studies carried out. R73 fails to complement
unc-15(
e1214), with R73/e1214 heterozygotes resembling R73 in their muscle structure by polarizing microscopy. This defect in muscle structure maps close to
dpy-5 I, and three factor crosses indicate that the mutation(s) lies near or to the right of
unc-13. No evidence for a mutation(s) in the
unc-54 gene was found. Thus R73 is apparently a partial revertant of an
unc-15 allele, probably
e73 and not
unc-54(
e569) (Where the error in bookkeeping occurred is unclear), and the large paracrystalline arrays, presumably of paramyosin, remain characteristic only of presumptive missense alleles of
unc-15.