Sequence diversity and conservation of the poly(A)-binding protein in plants

Although the poly(A)-binding protein (PABP) is relatively conserved among e ukaryotes, there is a surprising degree of divergence within the Arabidopsi s thaliana PABP gene family which is unique for any species investigated to date. To determine whether divergent PABPs are present in another dicot sp ecies and whether members of a PABP multigene family are conserved between plant species, cDNAs encoding PABP were isolated from Nicotiana tabacum,? a nd were compared with PABP from the Arabidopsis gene family as well as othe r plant species. Arabidopsis PAB2 is considerably more conserved with the t obacco (a dicot) and wheat (a monocot) PABPs so far isolated reflecting the evolution of higher plants whereas Arabidopsis PAB5 has diverged significa ntly from these plant PABPs. Analysis of individual domains within PABP dem onstrated that of the four N-terminal RNA recognition motif (RRM) domains i n Arabidopsis PAB5, RRM1, RRM2, RRM4 exhibit a higher degree of conservatio n with other plant PABPs whereas RRM3 and particularly the C-terminal domai n have diverged from the other higher plant PABPs analyzed. These data supp ort the hypothesis that PABP underwent gene duplication during plant evolut ion and that individual domains within PABP have evolved at different rates . (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.