Module M2 is formed by nucleotides located between bases G29 and C96 of the analyzed transcript and is composed of three helical regions, two 6 bp and one 14 bp in length. Each of these helical regions is resistant to enzymatic digestion and lead ion hydrolysis. The three helixes are separated by two asymmetric, internal loops (b and c), which are mapped very well by all probes used. The longest helical region includes as many as six non-WC, U-G and G-U base pairs. Four of these exist as two tandems: U-G, G-U and U-G, U-G, which are known to be potential metal-or protein-binding sites. The hairpin structure contains a small 3-nt terminal loop (5 0 -UAU), which is also well recognized by both lead ions and enzymes ( Figure 1A and B) . The M2 hairpin structure is conserved among species (Figure 2) , which suggests its significant role in regulation of transcript fate.