Current Protein and Peptide Science, 2000, 1, 49-73 49 1389-2037/00 $25.00+.00 © 2000 Bentham Science Publishers Ltd. Construction of Macromolecular Assemblages in Eukaryotic Processes and their Role in Human Disease: Linking RINGs Together A. Kentsis and K. L. B. Borden* Department of Physiology & Biophysics, Mount Sinai School of Medicine, New York University, New York, NY 10029, USA Abstract: Members of the Really Interesting New Gene (RING) family of proteins are found throughout the cells of eukaryotes and function in processes as diverse as development, oncogenesis, viral replication and apoptosis. There are over 200 members of the RING family where membership is based on the presence of a consensus sequence of zinc binding residues. Outside of these residues there is little sequence homology; however, there are conserved structural features. Current evidence strongly suggests that RINGs are protein interaction domains. We examine the features of RING binding motifs in terms of individual cases and the potential for finding a universal consensus sequence for RING binding domains (FRODOs). This review examines known and potential functions of RINGs, and attempts to develop a framework within which their seemingly multivalent cellular roles can be consistently understood in their structural and biochemical context. Interestingly, some RINGs can self- associate as well as bind other RINGs. The ability to self-associate is typically translated into the annoying propensity of these domains to aggregate during biochemical characterization. The RINGs of PML, BRCA1, RAG1, KAP1/TIF1β, Polycomb proteins, TRAFs and the viral protein Z have been well characterized in terms of both biochemical studies and functional data and so will serve as focal points for discussion. We suggest physiological functions for the oligomeric properties of these domains, such as their role in formation of macromolecular assemblages which function in an intricate interplay of coupled metal binding, folding and aggregation, and participate in diverse functions: epigenetic regulation of gene expression, RNA transport, cell cycle control, ubiquitination, signal transduction and organelle assembly. INTRODUCTION By virtue of relating organic and inorganic worlds, organometallic interactions play an exceedingly important role in living organisms, and undoubtedly present some of the most fascinating questions in biochemistry. This is particularly true of zinc, which due to its unique chemical activity and electronic structure is able to facilitate a diverse set of chemical reactions, and gives rise to proteins that constitute one of the largest families in eukaryotes. In spite of the presence of some proteins that bind zinc in both eu- and archae-bacteriae, these clades lack the diverse and numerous zinc-binding domains of eukaryotes, which number over 100 in yeast and more than 500 in Caenorhabditis elegans, implicating these organometallic macromolecules in eukaryotic as well as metazoan evolution [1]. *Address correspondence to this author at Department of Physiology & Biophysics, Box 1677, Mount Sinai School of Medicine, New York University, New York, NY 10029; Tel # 212-659-8677; 212-849-2456; e-mail kathy@inka.mssm.edu Of particular interest to us is a seemingly mysterious group of zinc-binding proteins termed Really Interesting New Genes (RINGs), with the first protein cloned on the basis of its location proximal to the MHC regions on chromosome 6. The RING has an unusual arrangement of cysteine and histidine residues [2] and this coordination consensus (Fig. 1) is similar to other zinc-binding proteins, namely LIM and PHD domains [3]. RINGs are specifically characterized by particular core residues in sequences intervening the metal binding sites, as well as their association with other structural motifs such as B-boxes. RING domains participate in a truly dazzling array of biochemical processes, including control of protein translation and ubiquitin-dependent degradation, signal transduction, cell cycle progression and apoptosis, regulation of transcription and mRNA transport-- traits that distinctively define metazoan organisms-- as well as in various human disease states, such as viral infection and cancer, which have also come to characterize metazoan life.