Unique features of plant cleavage and polyadenylation specificity factor revealed by proteomic studies

Cleavage and polyadenylation of precursor mRNA is an essential process for mRNA maturation. Among the 15 to 20 protein factors required for this process, a subgroup of proteins is needed for both cleavage and polyadenylation in plants and animals. This subgroup of proteins is known as the cleavage and polyadenylation specificity factor (CPSF). To explore the in vivo structural features of plant CPSF, we used tandem affinity purification methods to isolate the interacting protein complexes for each component of the CPSF subunits using Arabidopsis (Arabidopsis thaliana ecotype Landsberg erecta) suspension culture cells. The proteins in these complexes were identified by mass spectrometry and western immunoblots. By compiling the in vivo interaction data from tandem affinity purification tagging as well as other available yeast two-hybrid data, we propose an in vivo plant CPSF model in which the Arabidopsis CPSF possesses AtCPSF30, AtCPSF73-I, AtCPSF73-II, AtCPSF100, AtCPSF160, AtFY, and AtFIPS5. Among them, AtCPSF100 serves as a core with which all other factors, except AtFIPS5, are associated. These results show that plant CPSF possesses distinct features, such as AtCPSF73-II and AtFY, while sharing other ortholog components with its yeast and mammalian counterparts. Interestingly, these two unique plant CPSF components have been associated with embryo development and flowering time controls, both of which involve plant-specific biological processes.