FIGURE 1.

Complex formation between TruB or RluA and RNA stem–loops containing f⁵U by gel shift in SDS-PAGE. (A) Incubation of TruB (37.3 kD; marked with arrow) with [f⁵U]TSL does not result in a shifted band over a broad time range; TruB was present at 12.5 μM in all incubations; (MW) molecular weight standards. (B) Incubation of RluA (26.2 kD; marked with arrow) with [f⁵U]ASL produces a complex that survives denaturation by formamide and SDS (shifted band), with the amount of complex reflecting the ratio of enzyme to RNA. If the samples are heated before electrophoresis, the complex decomposes, and some decomposition is apparent even without heating.