MOLECULAR-CLONING OF A POU DOMAIN-CONTAINING FACTOR INVOLVED IN THE REGULATION OF THE BOMBYX SERICIN-1 GENE

The POU domain is a highly conserved region found in a number of trans cription factors and products of developmental control genes. We repor t here the isolation and characterization of a POU domain-containing c DNA (POU-M1) from the middle silk gland of Bombyx mori. It encodes a p rotein with a POU domain identical to that of the Drosophila Cf1-a pro tein. By mobility shift and nuclease protection assays, the POU-M1 pro tein and the putative silk gland factor 3 (SGF-3) were found to intera ct in an indistinguishable manner with the SC region (positions -204 t o -183) of the sericin-1 gene, a key cis-acting element involved in th e regulation of the gene through the interaction with SGF-3. Antibodie s raised against the synthetic oligopeptide corresponding to the COOH- terminal region of the putative POU-M1 sequence reacted specifically t o both the POU-M1 protein and SGF-3. Northern blot hybridization and W estern blotting revealed that POU-M1 expression is regulated both temp orally and spatially during silk gland development. We conclude that t he POU-M1 protein is SGF-3 and propose that the differential expressio n of the POU-M1 gene is probably involved in the transcriptional regul ation of the silk protein genes.