Arabidopsis thaliana poly (A) binding protein 2 (PAB2) functions in yeast translational and mRNA decay processes

The single yeast gene (PAB1) encoding poly (A) binding protein (PABP) has several roles in posttranscriptional processes, including translation initiation and mRNA decay. PABP is encoded by a large gene family in plants. Within Arabidopsis thaliana, the several characterized PABP genes exhibit an extreme degree of sequence divergence and are differentially expressed. Arabidopsis PAB2 is expressed in distinct tissues or during defined developmental windows in most plant organs. In this study we demonstrate that PAB2 restores viability to a yeast pab1 mutant strain. Yeast strains containing wildtype, null (PAB2(s)) and temperature sensitive (PAB2(ts)) alleles of PAB2 were used to explore the molecular functions of the plant protein. PAB2 can participate in poly (A) tail shortening, thus demonstrating that it interacts with the yeast poly(A) nuclease complex. PAB2 is required for translation, helping to maintain intact polysome structures. Consistent with its role in translation initiation, poly (A) was found to enhance PABP binding to Arabidopsis eIF-iso4G in vitro. In addition, PAB2 can partially restore the linkage between deadenylation, decapping and mRNA decay in yeast. Taken together, our results suggest that Arabidopsis PAB2 participates in many of the same complex post-transcriptional processes identified for yeast PAB1, and is functionally distinct from other characterized Arabidopsis PABPs.