Poly(A)-binding protein 1 (PABP1) has a fundamental role in the regulation of 
mRNA translation and stability, both of which are crucial for a wide variety of 
cellular processes. Although generally a diffuse cytoplasmic protein, it can be 
found in discrete foci such as stress and neuronal granules. Mammals encode 
several additional cytoplasmic PABPs that remain poorly characterised, and with 
the exception of PABP4, appear to be restricted in their expression to a small 
number of cell types. We have found that PABP4, similarly to PABP1, is a 
diffusely cytoplasmic protein that can be localised to stress granules. However, 
UV exposure unexpectedly relocalised both proteins to the nucleus. Nuclear 
relocalisation of PABPs was accompanied by a reduction in protein synthesis but 
was not linked to apoptosis. In examining the mechanism of PABP relocalisation, 
we found that it was related to a change in the distribution of poly(A) RNA 
within cells. Further investigation revealed that this change in RNA 
distribution was not affected by PABP knockdown but that perturbations that 
block mRNA export recapitulate PABP relocalisation. Our results support a model 
in which nuclear export of PABPs is dependent on ongoing mRNA export, and that a 
block in this process following UV exposure leads to accumulation of cytoplasmic 
PABPs in the nucleus. These data also provide mechanistic insight into reports 
that transcriptional inhibitors and expression of certain viral proteins cause 
relocation of PABP to the nucleus.