Human ACF1 Alters the Remodeling Strategy of SNF2h

Xi He,Hua-Ying Fan,Geeta J Narlikar,Robert E Kingston

doi:10.1074/jbc.m603008200

Xi He, Hua-Ying Fan + Show 2 more

Open Access

https://doi.org/10.1074/jbc.m603008200

Copy DOI

Abstract

The human ACF chromatin-remodeling complex (hACF) contains the ATPase motor protein SNF2h and the non-catalytic hACF1 subunit. Here, we have compared the ability of SNF2h and a reconstituted hACF complex containing both SNF2h and hACF1 to remodel a series of nucleosomes containing different lengths of DNA overhang. Both SNF2h and hACF functioned in a manner consistent with sliding a canonical nucleosome. However, the non-catalytic subunit, hACF1, altered the remodeling properties of SNF2h by changing the nature of the requirement for a DNA overhang in the nucleosomal substrate and altering the DNA accessibility profile of the remodeled products. Surprisingly, addition of hACF1 to SNF2h increased the amount of DNA overhang needed to observe measurable amounts of DNA accessibility, but decreased the amount of overhang needed for a measurable binding interaction. We propose that these hACF1 functions might contribute to making the hACF complex more efficient at nucleosome spacing compared with SNF2h. In contrast, the SWI/SNF complex and its ATPase subunit BRG1 generated DNA accessibility profiles that were similar to each other, but different significantly from those of hACF and SNF2h. Thus, we observed divergent remodeling behaviors in these two remodeling families and found that the manner in which hACF1 alters the remodeling behavior of the ATPase is not shared by SWI/SNF subunits.

Highlights

The SNF2 superfamily [1, 7]
To examine how non-catalytic subunits in a remodeling complex might alter the function of the central ATP-dependent subunit, we compared the ATPase SNF2h in isolation with the human ACF chromatin-remodeling complex (hACF) complex, which contains both SNF2h and the non-catalytic subunit hACF1
As anticipated from previous work, the hACF complex had higher activity compared with SNF2h alone in that hACF could move nucleosomes away from the starting position at lower concentrations than SNF2h alone (Fig. 1B)

Summary

Introduction

The SNF2 superfamily [1, 7]. These complexes are divided into at least four subfamilies defined by the ATPase catalytic subunits Swi2/Snf, ISWI, CHD, and Swr. Human complexes that contain the human ISWI homolog SNF2h include RSF (remodeling and spacing factor; contains SNF2h and RSF1), WICH (WSTFISWI chromatin remodeling; contains WSTF and SNF2h), hACF (ATP-utilizing chromatin assembly and remodeling factor; contains ACF1 and SNF2h), hCHRAC (chromatin accessibility complex; contains SNF2h, hACF1, p15, and p17), NoRC (nucleolar remodeling complex; contains SNF2h and TIP5), and the SNF2h/cohesin/NuRD complex (8 –13) This diversity in SNF2h-based complexes raises the question of the mechanistic role played by these different subunits in the process of nucleosome remodeling. SWI/SNF family complexes create products with characteristics distinct from those of canonical nucleosomes and are able to efficiently create access to sites near the center of the nucleosome. These observations have led to the hypothesis that these remodeling complexes function by distinct mechanisms. Initial data on directionality of movement have raised the possibility that partner proteins of ISWI might cause more substantive changes in remodeling outcome [27, 28, 30]

Objectives

Methods

Results

Conclusion