Effect ofestrogen ongeneexpression: Purification ofvitellogenin messenger RNA

Wereport initial studies onestrogen-mediat- edregulation ofeggyolkprotein synthesis intherooster. Egg yolk proteins arenormally synthesized asalarge precursor, vitellogenin, intheliver o thelaying hen;roosters synthesize vitellogenin onlywhentreated withestrogen. Polysomal RNA fromtheliver ofestrogen-treated roosters wastrans- lated inareticulocyte cell-free system, andthenewlysynthe- sized proteins wereidentified byahighly specific andsensi- tiveindirect immunoprecipitation reaction. Themessenger RNAthat specifies vitellogenin hasbeenpurified morethan 800-fold fromrooster liver polysomal RNAbyacombination ofmethods, including immunoprecipitation ofpolysomes andchromatography ofRNAonpoly(U)Sepharose. Inrecent years animportant approach hasbeendeveloped forstudying themolecular mechanisms bywhich hormones regulate geneexpression ineukaryotic organisms. Thegoal ofthis approach istostudy theregulatory effects ofhor- monesinvitro, andinvolves thefollowing steps: isolation of aspecific messenger RNA (mRNA)fromthetarget tissue after administration ofhormone; identification ofthis mRNA byitsability toprogram thesynthesis ofaspecific protein invitro; purification ofthespecific mRNAtohomo- geneity; useofthepuremRNAasatemplate forsynthesis of complementary DNA;and, finally, useofthecomplementa-