Analysis of gene duplication repeats in the myosin rod

The helical coiled-coil region of the myosin rod in the nematode Caenorhabditis elegans is a repetitive sequence 1094 amino acids long which contains 39 repeats of a 28-residue pattern. The repeats are extremely significant when compared with the statistical distributions expected, first for random sequences, and then for sequences with a typical seven-residue coiled-coil periodicity. New and improved statistical tests are used. The repeats are stronger in the first 350 residues of the rod (fragment S-2) than in the remainder. The corresponding DNA sequence of the unc-54 gene shows the same features, but they are less significant when judged by the number of identical bases than are the amino acid similarities, as measured by Dayhoff scores. The rod sequence shows strong evidence for a longer repeat unit of 196 residues, which may be related to the cross-bridge spacing of 143 A in muscle.