Analysis of the steroid receptor coactivator 1 (SRC1)-CREB binding proteininteraction interface and its importance for the function of SRC1

The transcriptional activity of nuclear receptors is mediated by coactivato r proteins, including steroid receptor coactivator 1 (SRC1) and its homolog ues and the general coactivators CREB binding protein (CBP) and p300. SRC1 contains an activation domain (AD1) which functions via recruitment of CBP and and p300. In this study, we have used yeast two-hybrid and in vitro int eraction-peptide inhibition experiments to map the AD1 domain of SRC1 to a 35-residue sequence potentially containing two oi-helices. We also define a 72-amino-acid sequence in CBP necessary for SRC1 binding, designated the S RC1 interaction domain (SID). We show that in contrast to SRC1, direct bind ing of CBP to the estrogen receptor is weak, suggesting that SRC1 functions primarily as an adaptor to recruit CBP and p300. In support of this, we sh ow that the ability of SRC1 to enhance ligand-dependent nuclear receptor ac tivity in transiently transfected cells is dependent upon the integrity of the AD1 region. In contrast, the putative histone acetyltransferase domain, the Per-Amt-Sim basic helix-loop-helix domain, the glutamine-rich domain, and AD2 can each be removed without loss of ligand-induced activity. Remark ably, a construct corresponding to residues 631 to 970, which contains only the LXXLL motifs and the AD1 region of SRC1, retained strong coactivator a ctivity in our assays.