<p>The K homology (KH) domain was first identified in the human heterogeneous nuclear ribonucleoprotein (hnRNP) K. An evolutionarily conserved sequence of around 70 amino acids, the KH domain is present in a wide variety of nucleic acid-binding proteins. The KH domain binds RNA, and can function in RNA recognition [<cite idref="PUB00035579"/>]. It is found in multiple copies in several proteins, where they can function cooperatively or independently. For example, in the AU-rich element RNA-binding protein KSRP, which has 4 KH domains, KH domains 3 and 4 behave as independent binding modules to interact with different regions of the AU-rich RNA targets [<cite idref="PUB00035579"/>]. The solution structure of the first KH domain of FMR1 [<cite idref="PUB00005961"/>] and of the C-terminal KH domain of hnRNP K [<cite idref="PUB00005962"/>] determined by nuclear magnetic resonance(NMR) revealed a beta-alpha-alpha-beta-beta-alpha structure. Proteins containing KH domains include:</p><ul><li>Bacterial and organelle PNPases [<cite idref="PUB00035580"/>].</li><li>Archaeal and eukaryotic exosome subunits [<cite idref="PUB00035581"/>].</li><li>Eukaryotic and prokaryotic RS3 ribosomal proteins [<cite idref="PUB00035582"/>].</li><li>Vertebrate fragile X mental retardation protein 1 (FMR1) [<cite idref="PUB00035583"/>].</li><li>Vigilin, which has 14 KH domains [<cite idref="PUB00035584"/>].</li><li>AU-rich element RNA-binding protein KSRP.</li><li>hnRNP K, which contains 3 KH domains.</li><li>Human onconeural ventral antigen-1 (NOVA-1) [<cite idref="PUB00021445"/>].</li></ul><p>More information about these proteins can be found at Protein of the Month: RNA Exosomes [<cite idref="PUB00035573"/>].</p> K Homology