Regulation by estrogen of the vitellogenin gene.

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Abstract
The vitellogenin gene is inactive in the liver of male Xenopus laevis [African clawed frog], unless exogenous estrogen is administered. Conventional doses of estradiol-17.beta. result in the appearance of new hepatic mRNA, some of which are encoded for vitellogenin. Much higher doses of the hormone (2 mg/frog per day for 4 days) are required to elicit maximal responses. The relative levels of membrane-bound polysomes and vitellogenin mRNA were determined as a function of time and dose of hormone. Translation of total polysomal RNA in a cell-free system derived from wheat germ was used to estimate the relative levels of vitellogenin mRNA. Faithful translation of this mRNA was indicated by 2 lines of evidence: labeled cell-free products were immunoprecipitated with antivitellogenin antibody, and the migration of the major labeled product in sodium dodecyl sulfate/acrylamide gels was identical to that of native vitellogenin. The results establish conditions for maximal estrogen-induced responses in this system, and are compatible with the hypothesis that a major regulatory mechanism of steroid hormones in the control of protein synthesis is that of gene activation and regulation of mRNA levels.