| Research Abstract |
Glucocorticoid-receptor complex (GRC) is a member of a superfamily of ligand-inducible transcription factors, and exert the effect by binding to chromosomal components, such as histones, non-histone proteins, nucleosomes and subsequently to specific DNA sequences (glucocorticoid response elements ; GREs). The GRC binding to chromatin is inhibited by macromolecular translocation inhibitors and enhanced by ATP-stimulated translocation promoter (ASTP) which we previously identified and purified from rat liver. ASTP is a histone binding protein which increases the GRC binding to nuclei or chromatin in the presence of ATP,but does not affect GRC binding to DNA-cellulose. Purified ASTP has a Mr of 93,000, as determined by gel filtration and is composed of two apparently identical subunits with a Mr of 48,000, as determined by SDS-PAGE.ASTP together with GRC binds to chromosomal components, such as histone H3 and H4, and the binding of ASTP and nucleosome may be involved in the formation of specific acceptor sites for GRC where their interaction with GRC may alter or disrupt nucleosomes for the binding of GRC to the GREs. In this project, we have cloned and sequenced a cDNA (2989 bp) encoding ASTP.An open reading frame of 524 amino acids encodes a protein with a molecular weight of 57 kDa. Amino acid sequences of a number of peptides obtained by Edman degradation of various cleavage products of the purified ASTP were identified in the cDNA-derived sequence. Northern analysis of mRNA from rat liver shows a major species of about 4.4.kb. Database searches indicate that this protein is not homologous to any identified protein of mammalian origin, however, high homology in the amino acid sequence in center region of ASTP is apparent between ASTP and glycerol kinase from Ecoli (48%). The region of homology with other species may help to define sites of protein-protein interaction, as well as sites of possible interaction of ASTP with ATP.
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