Effect of estrogen on gene expression in the chick oviduct

Mercurated UTP was used as a substrate for RNA polymerases in the in vitro transcription of chromatin so that newly synthesized RNA could be efficiently separated from endogenous chromatin RNA by means of sulfhydryl-Sepharose affinity chromatography. Utilizing this technique, it was possible to examine the effect of varying enzyme to DNA ratios on the transcription of specific genes from chromatin. For both Escherichia coli RNA polymerase and wheat germ RNA polymerase II, lowering the enzyme to DNA ration resulted in an increase in the percentage of ovalbumin mRNA sequences transcribed from chick oviduct chromatin. Similar results were also obtained for the transcription of the globin gene from chick reticulocyte chromatin. On the other hand, transcription of the globin gene from oviduct chromatin or the ovalbumin gene from reticulocyte chromatin or deproteinized chick DNA was not significantly affected by varying enzyme to DNA ratios. These results indicate that preferential transcription of certain chromatin genes relative to total RNA synthesis can occur and that this process is dependent on the presence of chromosomal proteins. Utilizing a cDNA probe complementary to the anticoding strand of the ovalbumin gene, the degree of asymmetry of the in vitro transcription of this gene was also examined. The percentage of ovalbumin RNA sequences homologous to the anticoding strand was not significantly affected when the enzyme to DNA ratio was lowered 16-fold. Since the percentage of coding ovalbumin mRNA sequences increased more than 6-fold over the same range, the percentage of asymmetric transcription of this gene increased. At the lowest enzyme to DNA ratio tested, the transcription of the ovalbumin gene from oviduct chromatin was almost totally asymmetric and, thus, closely resembled the pattern of gene transcription characteristic of the in vivo state.