Control of expression of silk protein genes.

At least three silk genes are specifically expressed in the posterior, and five other genes in middle, silk glands. The products of genes active in PSG include fibroin, L-chain fibroin and P25 protein. PSG genes as well as the Ser-1 gene, differing in structure, exhibit a striking degree of homology of their 5' flanking sequences. This suggests the presence of common regulatory mechanisms. The expression of silk protein genes is probably controlled by tissue-specific and general transcriptional factors. Hormones seem to participate in the regulation of expression of silk protein genes.