The ovalbumin gene: organization, structure, transcription, and regulation.

Publisher Summary This chapter discusses the regulation of expression of the chicken ovalbumin gene by steroid hormones. Upon entering the cell, steroid hormones are initially bound to specific cytoplasmic protein receptors. The hormone–receptor complex undergoes activation and translocates from the cytoplasm into the nucleus. In the nuclear compartment, the hormone–receptor complex binds to acceptor sites on the target cell chromatin. This is followed by the activation of specific genes resulting in the appearance of new species of RNA. The progesterone receptor of chick oviduct is a dimer composed of A and B subunits. This subunit structure has been confirmed by the use of a reversible cross-linking reagent that will cross-link the native dimer. After extraction and partial purification, the dimer can be dissociated, releasing equimolar amounts of the A and B proteins. The A protein has a molecular weight of 79,000, and that of the B protein is 117,000. Evidence indicates that the entire gene of ovalbumin gene is transcribed as a unit into a primary transcript of RNA that appears to be subsequently processed into mature mRNA by the reactions of precise cleavage and ligation. Thus, an abundant amount of intracistronic DNA will never be expressed in the phenotype as proteins. As the cell is under environmental pressure to construct proteins (enzymes) with a particular set of characteristics, the cell could have been encouraged to splice together new polypeptides via the assembly of various segments of DNA into a gene region.