Studies on the structure and function of chick-oviduct chromatin. 2. Biochemical characterization of two chromatin fractions isolated by ECTHAM-cellulose chromatography.

Chromatin prepared at various stages of hormone-mediated development of the chick oviduct was investigated for the relative proportions of transcriptionally active (fraction I) and repressed (fraction II) fractions by ECTHAM-cellulose chromatography. During primary stimulation with estrogen, the amount of chromatin DNA in fraction I plotted as a function of time of stimulation showed a bell-shaped profile, similar to the profile obtained earlier for the number of chromatin sites available to RNA polymerase for initiation of RNA synthesis. Chromatin form a transcriptionally inactive system, hen erythrocytes, eluted mainly (98%) as fraction II. The transcriptionally active fraction I of estrogen-stimulated oviduct contained a 4-fold greater RNA polymerase II activity than was found in fraction II. This could be explained by a differential inhibition of RNA polymerase activity in fraction II since enzyme preparations extracted and purified from both chromatin fractions showed equal activities. In support of this finding, fraction I eluted from ECTHAM-cellulose showed a 4-fold greater concentration of rifampicin-resistant RNA chain initiation sites as compared to fraction II. When chromatin from oviduct mince incubated with labeled progesterone and 17 beta-estradiol and was chromatographed on ECTHAM-cellulose, the transcriptionally active fraction also contained a 4-fold greater concentration of bound hormone (per weight DNA) as compared to the repressed fraction.