Evolutionary history exposes radical diversification among classes of interaction partners of the MLLE domain of plant poly(A)-binding proteins

Background Poly(A)-binding proteins (PABPs) are evolutionarily conserved proteins that have important functions in the regulation of translation and the control of mRNA stability in eukaryotes. Most PABPs encode a C-terminal domain known as the MLLE domain (previously PABC or CTC), which can mediate protein interactions. In earlier work we identified and predicted that four classes of MLLE-interacting proteins were present in Arabidopsis thaliana, which we named CID A, B, C, and D. These proteins encode transcription-activating domains (CID A), the Lsm and LsmAD domains of ataxin-2 (CID B), the CUE and small MutS-related domains (CID C), and two RNA recognition domains (CID D). We recently found that a novel class that lacks the LsmAD domain is present in CID B proteins.