The CUG-binding protein binds specifically to UG dinucleotide repeats in ayeast three-hybrid system

The CUG-binding protein (CUG-BP) has been reported to be involved in the pa thogenesis of myotonic dystrophy (DM) through binding to a CUG trinucleotid e repeat located in the 3' untranslated region (3'UTR) of the DM protein ki nase (DMPK) gene. We found that CUG-BP associates with long CUG; trinucleot ide repeats ((CUG)(11)(CUG)(12)), but not with short repeats ((CUG)(12)) in a yeast three-hybrid system. On the other hand, CUG-BP+LYLQ, an alternativ ely spliced isoform of CUG-BP, does not associate with CUG trinucleotide re peats regardless of the repeat length. In addition to these findings, we fo und that CUG-BP and CUG-BP+LYLQ strongly and specifically associate with UG dinucleotide repeats. Deletion analyse of CUG-BP revealed that the absence of the first or third RNA-binding domain (RBD I and RED III, respectively) does not affect the interaction between CUG-BP and UG dinucleotide repeats . Loss of the second RNA-binding domain (RBD II) decreases the affinity of CUG-BP for UG dinucleotide repeats by about 40%. Unexpectedly, deletion of the linker domain most severely reduces the interaction, although this regi on does not contain a known RNA-binding motif, Our results suggest the poss ibility that both CUG-BP and CUG-BP+LYLQ associate with UG repeat-containin g mRNAs and regulate such metabolic properties as mRNA localization, stabil ity, and translation, and provide new insights into the pathogenesis of DM. (C) 2000 Academic Press.