Immunological characterization of plant polyadenylate-binding proteins

We have raised antibodies against purified 70 kDa pea cytoplasmic polyadenylate-binding protein (PABP). These antibodies recognize both the 70 kDa PABP and a nuclear, 45 kDa PABP. They do not inhibit RNA binding by the purified 70 kDa PABP and do not recognize monocot or yeast PABPs, suggesting that they recognize epitopes distinct from the RNA-binding domains in these proteins. Using these antibodies, we have studied the expression of PABPs in pea during develpment and in different tissues. We find that both the cytoplasmic and nuclear PABPs are present in all tissues, and at all stages of development examined. However, the relative proportion of these two proteins is different in different tissues, with the cytoplasmic protein predominating in leaves and the nuclear protein in roots. Our antibodies also recognize two groups of proteins that appear during discrete stages of development in pea. One of these, apparent in old tissues, may be breakdown products of the cytoplasmic or nuclear PABPs. The other, which occurs only in cotyledons, cannot be assigned a function at this time.