The association of a La module with the PABP-interacting motif PAM2 is a recurrent evolutionary process that led to the neofunctionalization of La-related proteins.

La-related proteins are largely uncharacterized factors, well conserved throughout evolution. Recent reports on the function of human and suggest that these proteins fulfill key functions in mRNA metabolism and/or translation. We report here a detailed evolutionary history of the Lduanyu374 and 6 families in eukaryotes. Genes coding for Lduanyu374 and 6 were duplicated in the common ancestor of the vertebrate lineage, but one Lduanyu376 gene was subsequently lost in the common ancestor of the eutherian lineage. The Lduanyu376 gene was also independently duplicated several times in the vascular plant lineage. We observed that vertebrate Lduanyu374 and plant Lduanyu376 duplication events were correlated with the acquisition of a PABP-interacting motif 2 (PAM2) and with a significant reorganization of their RNA-binding modules. Using isothermal titration calorimetry (ITC) and immunoprecipitation methods, we show that the two plant PAM2-containing and c) can, indeed, interact with the major plant poly(A)-binding protein (PAB2), while the third plant Lduanyu376 is unable to do so. We also analyzed the RNA-binding properties and the subcellular localizations of the two types of plant Lduanyu376 proteins and found that they display nonredundant characteristics. As a whole, our results support a model in which the acquisition by Lduanyu374 and Lduanyu376 of a PAM2 allowed their targeting to mRNA and led to their neofunctionalization.

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