Role of dimerization in KH/RNA complexes: the example of Nova KH3.

The K homology module, one of the most common RNA-binding motifs, is present in multiple copies in both prokaryotic and eukaryotic regulatory proteins. Increasing evidence suggests that self-aggregation of KH modules has a functional role. We have used a combination of techniques to characterize the behavior in solution of the third KH domain of Nova-1, a paradigmatic KH protein. The possibility of working on the isolated module allowed us to observe specifically the homodimerization and RNA-binding properties of KH domains. We provide conclusive evidence that self-association of Nova-1 KH3 occurs in solution even in the absence of RNA. Homodimerization involves a specific protein/protein interface. We also studied the dynamical behavior of Nova-1 KH3 in isolation and in complex with RNA. These data provide a model for the mechanism of KH/RNA recognition and suggest functional implications of dimerization in KH complexes. We discuss our findings in the context of the whole KH family and suggest a generalized mode of interaction.