If this latter case is true, considering that Hax-1 has been identified as the same trans-acting factor for both vimentin and Pol b mRNAs, the hairpin element within the 3 0 UTR of the Pol b transcript may also represent a motif directing mRNA to the perinuclear space. Perinuclear localization of certain transcripts, and their subsequent translation at this site, could facilitate an efficient nuclear import of newly synthesized proteins (15, 16, 17) . DNA polymerase b as a nuclear protein could also benefit from such a mechanism.