Two-hybrid cloning identifies an RNA-binding protein, GRY-RBP, as a component of apobec-1 editosome

ApoB mRNA editing is mediated by an editosome complex with apobec-1 as its catalytic component. By yeast two-hybrid cloning using apobec-1 as bait we identified a 69.6-kDa RNA binding protein, GRY-RBP, that contains 3 RNA-rec ognition motifs (RRMs) as a novel apobec-1 associating protein. GRY-RBP may be an alternatively spliced species of NASP1, a protein of known function. GRY-RBP was shown to bind to; apobec-1, the catalytic component of apoB mR NA editosome, in vivo and in vitro. Immunodepletion using a monospecific ra bbit antibody abolished editing in apobec-1 expressing HepG2 S-100 extracts . GRY-RBD interacted with apobec-1 through its C-terminus. It contains thre e RRM (RNA recognition motifs) domains that are homologous to those found i n human ACF (apobec-1 complementation factor). Phylogeny analysis of the RR M domain-containing proteins indicates that GRY-RBP clusters with hnRNP-R, ACF, and ABBP-1 (another apobec-1 binding protein), In addition to its invo lvement with apobec-1 editosome, the suggested cellular functions of GRY-RB D and its structural homologues include RNA transport and RNA secondary str ucture stabilization, (C) 2001 Academic Press.