Targeting a SWI/SNF-related chromatin remodeling complex to the beta-globin promoter in erythroid cells.

Chromatin remodeling complexes such as the SWI/SNF complex make DNA accessible to transcription factors by disrupting nucleosomes. However, it is not known how such complexes are targeted to the promoter. For example, a SWI/SNF1-like chromatin remodeling complex erythroid Krüppel-like factor (EKLF) coactivator-remodeling complex 1 (E-RC1) disrupts the nucleosomes over the human beta-globin promoter in an EKLF-dependent manner. However, it is not known whether E-RC1 is targeted specifically to the beta-globin promoter or whether E-RC1 is randomly targeted, but its activity is evident only at the beta-globin promoter. Because E-RC1 cannot remodel chromatin over the beta-globin promoter without EKLF in vitro, it has been proposed that SWI/SNF1-like complexes such as E-RC1 are targeted specifically to the promoter by selectively interacting with promoter-associated transcription factors such as EKLF. In this report, we test this hypothesis in the cellular context by using the ProteIN POsition Identification with Nuclease Tail (PIN*POINT) assay. We find that the Brahma-related gene (BRG) 1 and BRG1-associated factor (BAF) 170 subunits of E-RC1 are both recruited near the transcription initiation site of the beta-globin promoter. On transiently transfected templates, both the locus control region and the EKLF-binding site are important for their recruitment to the beta-globin promoter in mouse erythroleukemia cells. When the beta-globin promoter was linked to the cytomegalovirus enhancer, the E-RC1 complex was not recruited, suggesting that recruitment of the E-RC1 complex is not a general property of enhancers.