Global insights into cellular organization and genome function require comprehensive understanding of the interactome networks that mediate genotype-phenotype relationships 1,2 . Here, we present a human "all-by-all" reference interactome map of human binary protein interactions, or "HuRI". With ~53,000 high-quality protein-protein interactions (PPIs), HuRI has approximately four times more such interactions than high-quality curated interactions from smallscale studies. Integrating HuRI with genome 3 , transcriptome 4 , and proteome 5 data enables the study of cellular function within most physiological or pathological cellular contexts. We demonstrate the utility of HuRI in identifying specific subcellular roles of PPIs. Inferred tissuespecific networks reveal general principles for the formation of cellular context-specific functions and elucidate potential molecular mechanisms underlying tissue-specific phenotypes of Mendelian Reprints and permissions information is available at http://www.nature.com/reprints.Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:http://www.nature.com/authors/editorial_policies/license.html#terms

The activity of DinB is governed by the formation of a multiprotein complex (MPC) with RecA and UmuD. We identified two highly conserved surface residues in DinB, cysteine 66 (C66) and proline 67 (P67). Mapping on the DinB tertiary structure suggests these are noncatalytic, and multiple-sequence alignments indicate that they are unique among DinB-like proteins. To investigate the role of the C66-containing surface in MPC formation, we constructed the dinB(C66A) derivative. We found that DinB(C66A) copurifies with its interacting partners, RecA and UmuD, to a greater extent than DinB. Notably, copurification of RecA with DinB is somewhat enhanced in the absence of UmuD and is further increased for DinB(C66A). In vitro pulldown assays also indicate that DinB(C66A) binds RecA and UmuD better than DinB. We note that the increased affinity of DinB(C66A) for UmuD is RecA dependent. Thus, the C66-containing binding surface appears to be critical to modulate interaction with UmuD, and particularly with RecA. Expression of dinB(C66A) from the chromosome resulted in detectable differences in dinBdependent lesion bypass fidelity and homologous recombination. Study of this DinB derivative has revealed a key surface on DinB, which appears to modulate the strength of MPC binding, and has suggested a binding order of RecA and UmuD to DinB. These findings will ultimately permit the manipulation of these enzymes to deter bacterial antibiotic resistance acquisition and to gain insights into cancer development in humans.