THE MOUSE POLY (C)-BINDING PROTEIN EXISTS IN MULTIPLE ISOFORMS AND INTERACTS WITH SEVERAL RNA-BINDING PROTEINS

The murine poly(C)-binding protein (mCBP) was previously shown to belo ng to the group of K-homology(KH) proteins by virtue of its homology t o hnRNP-K. We have isolated cDNA-splice variants of mCBP which differ by two variable regions of 93 bp and/or 39 +/- 3 bp respectively. Both variable regions are located between the second and third KH-domain o f mCBP. The characterization of a partial genomic clone enabled us to propose a model for the generation of the second variable region by th e use of a putative alternative spl ice signal. The mCBP mRNA is expre ssed ubiquitously and the protein is found predominantly in the nucleu s with the exception of the nucleoli. We have identified five proteins which interact with mCBP in the yeast two hybrid system: mouse y-box protein 1 (msy-1), y-box-binding protein, hnRNP-L, filamin and splicin g factor 9G8. The interaction between mCBP and splicing factor 9G8 was confirmed in vivo. These results suggest a function of mCBP in RNA me tabolism.