An Age-Specific 35-kDa Phosphoprotein Binds to a Repressor Element in the Ovalbumin Gene Promoter in the Avian Species Japanese Quail

Abstract

The ovalbumin (Ov) gene is expressed in the tubular gland cells of the avian oviduct in a specific manner under the control of developmental, tissue-specific, and hormonal cues. The expression is controlled by an array of positive and negative cis-acting elements present up to 1 kb upstream of its transcription start site. Our findings presented in this communication indicate that a well-characterized repressor element may be involved in active repression of the gene during aging. At least two proteins bind to the 25-bp sequence used in the present study encompassing the COUP adjacent repressor (CAR) element. The binding of one of the trans-acting factor that interacts with the repressor element increases during aging. This is accompanied by a decrease in transcription of the gene. The binding of the factor-to-repressor element decreases when expression of the Ov gene is induced by steroid administration. The factor has an approximate molecular weight of 35 kDa and is a phosphoprotein. It loses its ability to bind to DNA upon dephosphorylation. This makes it a potential target of various kinases/phosphatases that relay the various developmental, tissue-specific, and hormonal cues. The other trans-acting factor is a single-strand specific protein that interacts with the repressor element in an age-independent manner. These two proteins acting in conjunction may be involved in the repression of the Ov gene in old female birds where the lower circulating level of steroid hormones may be acting as an age-related cue.