This research concerns the hormonal regulation of the vitellogenins and the apolipoproteins of very low density lipoprotein. These proteins are synthesized in the avian liver in response to estrogenic stimulation and serve to transport lipid and other nutrients to the yolk for embryonic development. These proteins are of great interest as models for the study of estrogen action and because of their roles in lipid transport. This proposal is largely focused on the regulation of apolipoprotein II (apo II) gene expression. Apo II is a major protein component of the very low density lipoprotein particles synthesized in response to estrogen. The estrogen-stimulated synthesis of apo II involves activation of gene transcription and a marked cytoplasmic stabilization of apo II mRNA. Experiments will be carried out to examine the estrogen-mediated stabilization of apo II mRNA and to test the hypothesis that stabilization is due to site specific interactions between stabilization factors and apo II mRNA. The research will be directed to three major questions. First, how is apo II mRNA structure related to functional aspects of its expression? These studies will require elucidation of the heterogeneity found at the 5' and 3' ends of the mRNA and an analysis of apo II mRNA secondary structure. A new method for high resolution mapping of mRNAs with base and struture specific ribonucleases has been developed for this purpose. Second, What is the pattern of protein binding on the mRNA and how does it relate to secondary structure and stabiliztion of apo II mRNA? Nuclease mapping will be used to determine sequences that are altered as a result of interaction with protein. Third, do apo II messenger ribonucleoprotein particles contain proteins unique to this mRNA? Are such proteins involved in estrogen-mediated stabilization. These particles will be purified and the proteins analyzed. Monoclonal antibodies to apo II mRNP proteins will be used to determine which proteins are unique to apo II mRNA, which are common to etrogen-regulated mRNAs, and which are common to all mRNAs. The long-term goal is to understand how estrogen-mediated stabilization of mRNA occurs. This is a major action of estrogens that has received relatively little attention.
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