A three-way junction and constituent stem-loops as the stimulator for programmed -1 frameshifting in bacterial insertion sequence IS911

Several signals are required for the programmed frameshifting in translatio n of IS911 mRNA. These include a Shine Dalgarno (SD)-like sequence, a slipp ery sequence of six adenine residues and a guanine residue (A6G) and a 3' s econdary structure. The structure of the mRNA containing these elements was investigated using chemical and enzymatic probing. The probing data show t hat the 3' structure is a three-way junction of stems. The function of the three-way junction was investigated by mutagenesis. Disrupting the stabilit y of the structure greatly affects frameshifting and transposition levels a s tested by separate ill vivo assays. Structural probing and thermal meltin g profiles indicate that the disrupted three-way junctions have altered str uctures. (C) 1999 Academic Press.