Efficient transcription requires an intact PBP-1 element.
(A) Schematic of the templates used for the
transcription assays. Shown are a 20-bp tag in the coding region
(cross-hatched), the transcribed region (dotted), the −10- to −1-bp
initiator region (INR), the 10-bp substitution of the PBP-1 element
(diagonal lines), and the sequences that replace the large Δ-Mut
(checkered). (B) Transcription activity assays. In
addition to the tagged SL gene, all reactions contain a similarly
tagged U6 snRNA gene. Equal amounts of U6 snRNA transcription in each
reaction ensured consistent extract activity. WT SL templates amounts
were 50 (lane 1), 20 (lane 2), and 10 ng (lane 3). Identical titrations
of S-Mut template or Δ-Mut are shown in lanes 4–6 and 7–9,
respectively.