Fig. 2.—

Classification of the mutational classes. Phenotypes are determined for pairs of complementary sequences (black: + strand, red: − strand), and are coarse grained to presence/absence of 5′-dangling end, catalytic structure, 3′-dangling end. As different phenotypes may fall in the same functional class, some of all the possibilities are depicted (the larger ones are the most frequent configurations). “Helpers” are defined by having a 5′-dangling end and the catalytic structure on at least one (and the same) strand, and not having a 3′-dangling end in both strands. “Stallers” are defined by having a 5′-dangling end but no catalytic structure on at least one (and the same) strand, and not having a 3′-dangling end in both strands. “Junk” are sequences that do not have any 5′-dangling end on either strands, and no 3′-dangling end on at least one. “Hybrid” sequences display a helper-like phenotype on one strand and staller-like on the other.