Repeated DNA sequences near the 5'-end of the silk fibroin gene.

Four different repeated sequence elements have been found in cloned silk moth DNA, extending from 5700 base pairs upstream from the silk fibroin gene to 600 base pairs within its intervening sequence. Only 2 of the 12 overlapping restriction fragments examined, ranging from 164 to 1800 base pairs in length, do not contain a repeated sequence. The 830 base pairs adjoining the 5'-end of the fibroin gene hybridize with only one sequence in the Bombyx mori genome. Fibroin gene transcription initiates within this single-copy DNA at least 500 base pairs downstream from any repeated DNA sequence. The data show that repeated sequences comprise a major portion of the DNA flanking this developmentally regulated gene but not the DNA immediately 5' to it; that an intervening sequence can contain a repeated element; and that repeated sequences can be interspersed with one another as well as with single-copy DNA in a typical animal genome. In addition, filter transfer hybridization can be used to quantitate repetition frequency and sequence divergence and to distinguish patterns of repeated sequence organization.