Fip1 - an interaction hub that links several polyadenylation factor subunits to poly(A) polymerase
One Arabidopsis gene whose product resembles a mammalian and yeast polyadenylation factor subunit is the so-called AtFip1(V) gene (1). The encoded protein bears a number of similarities to its human counteraprt - it binds RNA (with a modest preference for RNAs containing an FUE), it alters the activity of poly(A) polymerase, and it interacts with a number of other Arabidopsis polyadenylation factor subunits (see Figure 1). Among he latter are two (AtCFIm-25 and a nuclear poly(A) binding protein) that have not been reported to interact with Fip1 in other systems. These results suggest a model in which AtFip(V) is the center of a network of RNA-binding proteins and other factors that are involved in mRNA 3' end formation. They also provide conceptual links of a number of Arabidopsis proteins to poly(A) polymerase, thus strengthening the supposition that these proteins are authentic polyadenylation factor subunits.
Figure 1. Summary of protein-protein interactions amongst Arabidopsis polyadenylation factor subunits that have been reported in the literature. Interactions are denoted as lines connecting the various subunits. The AtPAP-AtCPSF100 interaction was reported by Elliott et al. (2) and the AtCst77-AtCstF64 interaction by Yao et al. (3); the others are described in Forbes et al. (1) and Addepalli and Hunt (4). Black circles denote proteins that bind RNA.
References
1. Forbes KP, Addepalli B, Hunt AG. 2006. An Arabidopsis Fip1 homologue interacts with RNA and provides conceptual links with a number of other polyadenylation factor subunits. J. Biol. Chem. 281: 176-186.
2. Elliott BJ, Dattaroy T, Meeks-Midkiff LR, Forbes KP, Hunt AG. 2003. An interaction between an Arabidopsis poly(A) polymerase and a homologue of the 100 kDa subunit of CPSF. Plant Mol. Biol. 51:373-84
3. Yao Y, Song L, Katz Y, Galili G. 2002. Cloning and characterization of Arabidopsis homologues of the animal CstF complex that regulates 3' mRNA cleavage and polyadenylation. J. Exp. Bot. 53:2277-8.
4. Addepalli B, Hunt AG. 2007. A novel endonuclease activity associated with the Arabidopsis ortholog of the 30-kDa subunit of cleavage and polyadenylation specificity factor. Nucl. Acids Res 35, 4453-63.