Thirteen Escherichia coil clones containing the whole or a part of the fibroin gene (16 kilobases long) have been isolated. The starting material was DNA extracted from the posterior silk glands of Bombyx mor. Most clones were obtained from sheared DNA fragments linked by poly(dA) poly(dT) joints to the plasmid pMB9. One of them includes the 5'end of the fibroin gene with a flanking sequence of 12 kilobases,