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In the laying hen the egg yolk proteins are synthesized in the liver. Some of these proteins, such as vitellogenin, are synthesized exclusively by the hen, while others, such as low density lipoprotein, are also synthesized by the rooster, but at a very low rate. Treatment of the rooster with estradiol, however, results in synthesis of the complete spectrum of egg yolk proteins at a rate comparable to that characteristic of the hen. We are interested in mechanisms that coordinate regulation of this group of estrogen-responsive genes and to this end have developed a procedure for selecting and cloning members of the group that exhibit common induction ratios. Complexity analyses carried out on total RNA isolated from rooster liver at different stages of the vitellogenic response suggested that the family of the estrogen-inducible mRNA species was located primarily in the abundant and intermediate complexity classes of mRNA and that the population of the complex class remained essentially unchanged throughout the vitellogenic response. This conclusion was confirmed by more detailed analyses using isolated cDNA fractions corresponding to individual abundance classes. We have used the information provided by these analyses to isolate cDNA probes specific for estrogen-inducible sequences of a particular abundance and exhibiting a particular induction ratio. The first probe that we have isolated in this fashion is specific for sequences that are induced by estrogen at least lOOO-fold. It is composed predominantly of sequences derived from two species of mRNA, vitellogenin and another, as yet uncharacterized mRNA, approximately 800 nucleotides long. pis cDNA probe has been used in the selection and isolation of cDNA clones containing both of these sequences.
King et al. (Sun,) studied this question.