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 s everal roles in posttranscriptional processes, including translation initia tion and mRNA decay. PABP is encoded by a large gene family in plants. With in Arabidopsis thaliana, the several characterized PABP genes exhibit an ex treme degree of sequence divergence and are differentially expressed. Arabi dopsis PAB2 is expressed in distinct tissues or during defined developmenta l windows in most plant organs. In this study we demonstrate that PAB2 rest ores viability to a yeast pab1 mutant strain. Yeast strains containing wild type, null (PAB2(s)) and temperature sensitive (PAB2(ts)) alleles of PAB2 w ere used to explore the molecular functions of the plant protein. PAB2 can participate in poly (A) tail shortening, thus demonstrating that it interac ts with the yeast poly(A) nuclease complex. PAB2 is required for translatio n, helping to maintain intact polysome structures. Consistent with its role in translation initiation, poly (A) was found to enhance PABP binding to A rabidopsis eIF-iso4G in vitro. In addition, PAB2 can partially restore the linkage between deadenylation, decapping and mRNA decay in yeast. Taken tog ether, our results suggest that Arabidopsis PAB2 participates in many of th e same complex post-transcriptional processes identified for yeast PAB1, an d is functionally distinct from other characterized Arabidopsis PABPs.