A 21 KDa protein resides in the nucleosomes of micrococcal nuclease sensitive liver chromatin of Atlantic salmon treated with estradiol.

Atlantic salmon was treated with 17-beta-estradiol to induce the process of vitellogenesis in liver. When the isolated liver nuclei were incubated with micrococcal nuclease at increasing enzyme/DNA ratios a 21 KDa protein appeared in the nuclease sensitive chromatin, the S-fraction. After HPLC gel filtration the 21 KDa protein resided with the oligo- and mononucleosomes. The S-fraction contained vitellogenin gene sequences at low nuclease/DNA ratios. The sequences were detectable also in the mononucleosomes derived from the S-fraction. After hormone treatment the vitellogenin gene exposed a higher sensitivity to micrococcal nuclease than the hormone-untreated controls. The results indicate that the 21 KDa protein took part in the hormone-mediated changes in gene expression by modulating the structure of estradiol responsive chromatin domains including the vitellogenin gene.