Evidence for periodicity in the amino-acid sequence of myosin.

We have characterized CNBr digests of rabbit myosin heavy chain, total rod, light meromyosin and mouse heavy chain by combined isoelectric focusing and dodecylsulfate gel electrophoresis. Conditions for digest were chosen so as to have less than complete cleavage at most or all of the methionine residues. Examination of the gels in the dodecylsulfate dimension shows a remarkable periodicity in the molecular weights of fragments produced in all these digests. Nearly all lie in a monotonic sequence with an interval of approximately 3800 between them. One interpretation of this finding is that there is a high degree of periodicity in the position of methionines of, at the very least, the light meromyosin region. The impression of periodicity is further re-inforced by a regular distribution of fragments in the isoelectric focusing dimension of the gels as well as in the dodecylsulfate dimension. The heterogeneity in the isoelectric focusing dimension could, unlike that in the dodecylsulfate dimension, be artefactual (e.g. as a consequence of de-amidation and or cyanylation) or as a result of protein heterogeneity due to gene duplication. However, it is also possible that it too reveals a periodicity, this time in the distribution of charged residues in the amino-acid sequence.