Probing data demonstrated that the short 3 0 UTR of Pol b transcript forms three separate structural modules, designated M1-M3 ( Figure 1B) . Module M1 represents a small hairpin structure with a C-rich terminal loop. The 3 0 -part of this structure is efficiently hydrolyzed with lead ions, even at a low concentration of the probe, which suggests that M1 hairpin has binding capacity for this metal ion. Module M3 contains the polyadenylation signal, followed by the cleavage and polyadenylation site, so only a part of it is present in the mature short Pol b transcript, which implies minor importance of the whole M3 module as a post-transcriptional regulatory element.