Mutagenic activity of the V(D)J recombinase is controlled by regulated access to target antigen receptor loci and generation of double-strand DNA breaks only after joint recognition of paired recombination signal sequences (RSS). We have recapitulated both key aspects of recombinase regulation in a cell-free system using plasmid substrates assembled into chromatin. We found that recruitment of the SWI/SNF chromatin remodeling complex to both RSS was required to increase coupled-cleavage. SWI/SNF functioned by altering local chromatin structure as measured by restriction endonuclease accessibility in the absence of transcription or histone modification. These observations set the baseline for future studies aimed at studying the role of specific histone modifications for the initiating step of V(D)J recombination.
