Silkmoth chorion multigene families constitute a superfamily: comparison of C and B family sequences.

We have characterized a new family of silkmoth chorion genes, called C, which is distinct from previously characterized A and B families. The amino acid compositions of 18 purified C proteins have been determined. Three subgroups are recognized on the basis of compositional similarities and may correspond to distinct gene families or subfamilies. The sequences of two overlapping cDNA clones have been determined in their entirety and shown to correspond to a C-specific sequence. Obvious homology is observed between the middle portions of the C sequence and previously characterized B sequences. By contrast, the arms of the C sequence share no significant similarities either with each other or with the corresponding arms of B sequences. Thus, the same tripartite structure originally observed in A and B family sequences is also present in the C family and may have functional significance. Secondary structure prediction of the C sequence is presented and supports this conclusion. The observed homology between C and B family sequences clearly establishes that silkmoth chorion multigene families constitute a superfamily.