FIG. 5.

Heterodimer formation provides direct evidence for a complementary loop-loop interaction at each DIS locus. Mutant RNAs were synthesized in which the four central palindromic nucleotides of DIS-1 or DIS-2 (Fig. 1B) were replaced by the indicated sequences in the context of either RNA-1 (280 bases) or RNA-4 (475 bases). These were then assayed for dimerization alone or in combination (at 1.5 nM each) after preincubation at the temperatures indicated. Above lanes in which two different RNAs were combined, the sequences of their central bases are shown in antiparallel alignment, with dots indicating any expected base pairing. M and D, monomers and homodimers, respectively, of the long (L) and short (S) RNAs; HD, heterodimers. Panels A and B were derived from two separate representative experiments done with different combinations of mutants.