Novel B family sequence from an early chorion cDNA library of Bombyx mori

A cDNA library has been constructed from transcripts present during the early stages of choriogenesis in the silk-moth, Bombyx mori. Clones representing novel sequences were selected by screening the library with (i) homotypic cDNA, (ii) rDNA and typical chorion probes of the A and B multigene families and (iii) selected clones from the library, which were positive in step (i) but negative in step (ii); this third step identified clones that hybridized to distinct subsets of the library. The sequence of one such clone was determined and shown to represent a novel subfamily of the B chorion multigene family, exclusively expressed during the early choriogenic period.