FIGURE 1.

Comparison of Rpo41p and T7 RNAP. Regions of homology between the phage and mitochondrial RNAPs are represented as boxes labeled A–L (4); substantial insertions in the sequences are represented by loops. The consensus sequences of the phage T7 and S. cerevisiae (S.c.) mitochondrial promoters are aligned relative to their start sites at +1 (bent arrows). Positions that determine specificity are underlined; single underline indicates positions at which substitutions reduce promoter strength by at least a factor of 3; the double underline indicates positions at which substitutions lead to at least a 10-fold reduction (18, 19, 29, 30). Interactions of the three elements in T7 RNAP that are primarily responsible for promoter recognition and melting are shown by arrows (solid arrow, specificity loop; dashed arrow, intercalating loop; dotted arrow, AT-rich recognition loop) (13). Asterisks below the Rpo41p scheme indicate the location of residues in Rpo41p that have been implicated in interactions with Mtf1p (31, 32).