Interaction of two multifunctional proteins - Heterogeneous nuclear ribonucleoprotein K and Y-box-binding protein

The heterogeneous nuclear ribonucleoprotein (hnRNP) K, a component of the h nRNP particles, appears to be involved in several steps of regulation of ge ne expression, To gain insight into mechanisms of K protein action, we perf ormed two-hybrid screens using full-length hnRNP K as a bait. Several novel protein partners were identified, including Y-box-binding protein (YB-1), splicing factors 9G8 and SRp20, DNA-methyltransferase, hnRNP L, and hnRNP U . In vitro binding studies and co-immunoprecipitation from cellular extract s provided evidence for direct interaction between hnRNP K and YB-1. Two di stinct domains in YB-1 were responsible for binding to K protein. Each prot ein was able to transactivate transcription from a polypyrimidine-rich prom oter; however, this effect was reduced when K and YB-1 proteins were coexpr essed suggesting a functional ineeraction between these two proteins.