Synthesis of [ 3 H]DNA Complementary to Ovalbumin Messenger RNA: Evidence for Limited Copies of the Ovalbumin Gene in Chick Oviduct

Accumulation of ovalbumin messenger RNA in chick oviduct is absolutely dependent upon estrogen. After estrogen treatment, ovalbumin comprises 60-65% of the total oviduct protein. We used maximally stimulated animals to extract and partially purify the ovalbumin messenger RNA. The final product was enriched about 100-fold in activity with respect to this specific messenger RNA. This ovalbumin messenger RNA fraction was used to direct the synthesis of a complementary [ 3 H]DNA in the presence of RNA-dependent DNA polymerase isolated from avian myeloblastosis virus. The complementary [ 3 H]DNA (specific radioactivity, 8 × 10 7 cpm/μg) was a faithful transcript since about 90% would hybridize back to the original messenger RNA template. Ovalbumin complementary [ 3 H]DNA was reannealed with an excess of chick-oviduct total DNA. The kinetics of this reaction indicate that only one copy of the ovalbumin gene exists in each haploid genome. These data suggest that estrogen may affect the oviduct genome to stimulate production of large numbers of ovalbumin messenger RNA molecules from a single copy of the ovalbumin gene.