The Arabidopsis ortholog of the 77 kDa subunit of the cleavage stimulatory factor (AtCstF-77) involved in mRNA polyadenylation is an RNA-binding protein.

The 77 kDa subunit of the polyadenylation cleavage stimulation factor (CstF77) is important in messenger RNA 3' end processing. Previously, we demonstrated that AtCstF77 interacts with AtCPSF30, the Arabidopsis ortholog of the 30 kDa subunit of the Cleavage and Polyadenylation Specificity Factor. In further dissecting this interaction, it was found that the C-terminus of AtCstF77 interacts with AtCPSF30. Remarkably, we also found that the C-terminal domain of AtCstF77 possesses RNA-binding ability. These studies therefore reveal AtCstF77 to be an RNA-binding protein, adding yet another RNA-binding activity to the plant polyadenylation complex. This raises interesting questions as to the means by which RNAs are recognized during mRNA 3' end formation in plants.