RNA is a major determinant of PABP nucleocytoplasmic localization
(A) Association of PABPs with translation complexes (represented by ribosomes) and/or mRNA prevents its availability for import. Complexes with other proteins (X; e.g. PABP-interacting protein (Paip)2) may also maintain its cytoplasmic steady state. Once released, PABP can be bound by the importin α/β complex which mediates the classical nuclear import pathway. It is possible that imported PABP may normally rapidly bind to newly synthesized poly(A) tails. (B–D) PABP export from the nucleus. (B) Cytoplasmic eEF1α facilitates PABP export by an unknown mechanism (represented by ‘?’). PABP exported by this pathway may be bound to mRNAs since it is dependent on ongoing transcription. (C) PABP exits the nucleus bound to mRNAs via the mRNA-export pathway which is mediated by a complex containing TAP. (D) PABP (perhaps mRNA-associated) exits the nucleus bound to paxillin via the classic CRM1 export pathway. This is likely to represent a minor pathway. Blue: nucleus with pores depicted as breaks in the surrounding blue line; grey: cytoplasm.