Structural Analysis of the C-Terminal RNA Binding Domain of CPEB3

Abstract

Cytoplasmic polyadenylation element binding protein isoform 3 (CPEB3) is a translational regulatory protein. There are four isoforms of CPEB. CPEB1 binds to a uracil rich cytoplasmic polyadenylation element (CPE) sequence in the 3’UTR of mRNA and upon phosphorylation switches from an inhibitor to an activator of translation through regulation of polyadenylation. CPEB3 does not promote polyadenylation nor does it bind to the CPE sequence. Rather, CPEB3 recognizes a structured RNA motif in the 3’UTR and inhibits translation. CPEB comprises an N-terminal kinase-binding region, two RNA recognition motifs that function in molecular recognition and a C-terminal zinc finger that doe not influence specificity, but is required for binding RNA. Our initial research is focused on the recognition of a structured mRNA by CPEB3 for comparison with parallel studies of CPEB1 bound to a single stranded CPE sequence. We have cloned, expressed and purified the isotope labeled RNA binding region of CPEB3. Preliminary structural studies and assays of the RNA binding activity are presented.