Correlations between the activities of DNA polymerase alpha and the glucocorticoid receptor.

Abstract

Specific inhibitors and anti-DNA polymerase a IgG have been utilized to probe for similarities between cytoplasmic rat hepatic glucocorticoid receptors and DNA polymerase a [DNA nucleotidyltransferase (DNA-directed) [1,2-3H]hydrocortisone to serum transcortin. The most obvious interpretation of these data is that cytoplasmic glucocorticoid receptors and DNA polymerase a share antigenic determinants. An alternative interpretation is that the polyclonal anti-DNA polymerase a antibody contains IgG molecules raised against calf thymus cytoplasmic activated glucocorticoid-receptor complexes that copurified with DNA polymerase a used as the antigen. Taken collectively, however, the antibody and inhibitor data suggest a relationship between DNA polymerase a and the glucocorticoid receptor.The precise mechanism by which glucocorticoids, and steroid hormones in general, elicit different specific phenotypic responses in target cells is not completely understood. However, it is clear that most, if not all, of these effects are mediated through cytoplasmic receptors that bind glucocorticoids with high affinity and specificity. Once the steroid has been bound, the glucocorticoid-receptor complex must then undergo a twostep process in order to bind to nuclei. The first step, termed "activation" or "transformation," is temperature dependent and involves a conformational change resulting in the exposure of positively charged residues on the surface of the molecule and an increased affinity for polyanions such as DNA. The second step, termed "translocation," is temperature independent and involves the movement of the "activated" complexes to the nucleus, where they bind to acceptor sites within the chromatin. Ultimately these nuclear bound complexes induce changes in chromatin structures, resulting in increased transcription and ultimate translation of specific mRNAs (1, 2 t To whom reprint requests should be addressed. 4555The publication costs ofthis article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact.

Immunocytochemical localization of chick DNA polymerases α and β+

“…However, it is extremely difficult to obtain a homogeneous preparation of this enzyme in large quantity and thus this antiserum may have contained an antibody against cytoplasmic protein present in the DNA polymerase a preparation. More recently, the same group (Schmidt et al, 1982) reported that their anti-DNA polymerase a IgG cross-reacted with cytoplasmic rat hepatic glucocorticoid receptors. This cross-reaction may be another reason for the cytoplasmic immunofluorescence observed.…”