Comparison of the hairpin motifs in vimentin and Pol b mRNAs did not reveal any significant similarities, which could suggest substrate requirements for Hax-1 binding. The presence of U-rich single-stranded regions (vimentin: AGUUUU in the terminal loop, Pol b: AGUUAU in the internal loop) represents the only similarity between the two structures, but the helical regions adjacent to this U-rich sequence in the Pol b mRNA are not evolutionarily conserved. The lack of similarities suggests that Hax-1-binding mechanism and affinities might be different for these two structures.