Gene expression of two fibroin alleles in the hybrid silkworm, J-131/Nd(2).

Fibroin gene expression in the posterior silk gland of normal strain (J-131/J-131), Nd strain (Nd(2)/Nd(2)) and their hybrid (J-131/Nd(2)) silkworms was compared on the levels of fibroin and fibroin mRNA production. The syntheses of both fibroin and fibroin mRNA in the Nd(2) and the hybrid silkworms were greatly reduced when compared with those of the normal silkworm. This result indicates that the Nd(2) gene represses dominantly fibroin gene expression, presumably at the level of transcription of fibroin gene. Estimation of gene products (fibroin and fibroin mRNA) from two fibroin alleles, Fnor and SNd, of the hybrid silkworm, J-131/Nd(2), demonstrates that the expression of the fibroin allele SNd derived from Nd(2) mutant strain is more severely repressed than that of the fibroin allele Fnor derived from J-131 strain.