Hormonally induced alterations of chromatin structure in the polyadenylation and transcription termination regions of the chicken ovalbumin gene.

We have studied the chromatin structure of a 16-kb region of the chicken genome containing the 3'-terminal 2 kb of the ovalbumin pre-mRNA coding sequence and the 14-kb segment located immediately downstream from the main mRNA polyadenylation site. Using the indirect end-labelling technique, four major and two minor DNase I-hypersensitive regions were found in the oviduct chromatin, whereas they were not present in liver, kidney or erythrocyte chromatin. The first hypersensitive region (region A) was present in chromatin of oviducts from laying hen and estrogen- or progesterone-stimulated immature chicks, in which the ovalbumin gene is expressed, but not in the chromatin of 'acute withdrawn' chicks where the gene is no longer transcribed. Region A spans 1.3 kb, from 7.2 to 8.5 kb downstream from the ovalbumin gene capsite (position +1), and encompasses the 3' moiety of the last exon including the major polyadenylation signal and polyadenylation site located at +7546 and +7564, respectively. Region A also contains a minor polyadenylation signal present at +7294 and the corresponding polyadenylation site at +7368. Two putative termination sequences at +8445 and +8483 are also found at the 3' extremity of region A in a 170-bp DNA segment within which 90% of the ovalbumin primary transcripts apparently terminate. Two minor hormone-independent DNase I-hypersensitive regions (a1 and a2) located at +8.6 and +8.8 kb are also specific to oviduct chromatin.(ABSTRACT TRUNCATED AT 250 WORDS)

Steroid hormone dependence of four DNase I-hypersensitive regions located within the 7000-bp 5'-flanking segment of the ovalbumin gene.

Four DNase I-hypersensitive regions (I-IV) occur in the 5'-flanking region of the ovalbumin gene in hen oviducts. One is centered close to the cap site (position +1) of transcription and the others at -0.8, -3.3 and -6.0 kb. The correlation of hypersensitivity with transcription was determined for each region in oviducts of chicks, where expression of the ovalbumin gene can be controlled by administration and withdrawal of steroid hormones. DNase I-hypersensitive regions were mapped by the indirect end-labeling technique and ovalbumin mRNA levels were determined by the dot blot assay. Diethylstilbestrol (DES) induces the appearance of hypersensitive regions I-IV whereas progesterone induces regions I, II and IV, but not region III. Upon withdrawal, regions II and III, and most of regions I and IV, disappear. A weak zone of hypersensitivity in region I near the cap site persists during withdrawal and a new zone of hypersensitivity appears between regions I and II. There is strong correlation between hypersensitivity at regions I-IV and gene transcription; ovalbumin mRNA levels are high in stimulated chicks, where hypersensitive regions are present, and drop to very low levels in withdrawn chicks, where the hypersensitivity is absent. We suggest that proteins, perhaps hormone receptors acting together with tissue-specific factors, induce DNAse I-hypersensitive regions I-IV of the ovalbumin gene.