We propose to study the hormonal regulation of gene expression in normal rat mammary tissue and in two rat mammary cancer model systems: the DMBA-induced mammary carcinoma and the transplantable R323OAC mammary carcinoma, each of which has characteristics in common with the human disease. Our investigation will coordinate a study of chromatin biochemistry, emphasizing the role of the nonhistone acidic chromosomal proteins, with an examination of unique sequence DNA transcription, and specific messenger RNA synthesis. Specific emphasis will be placed on the importance of estrogen and prolactin as gene regulators. Both of these hormones appear to play a major role in mammary gland differentiation and in the induction, growth and regression of mammary carcinoma. Our studies will be performed both in vivo and in vitro utilizing ovariectomized animals, an organ culture system, and epithelial cell suspensions obtained by collagenease treatment. We will analyze chromatin composition and transcriptional capacity and attempt to characterize the chromatin-associated molecules responsible for both specific gene expression and hormonal regulation. Coupled with these studies, we will apply the latest techniques of molecular hybridization to investigate unique sequence DNA transcription. The regulation of casein mRNA synthesis will be studied by direct isolation and translation in a cell-free system. We believe that significant advances in our understanding of the hormonal regulation of mammary cancer will come from such studies of nuclear gene expression.