Figure 3.

Promoter-mtRNAP interactions within transcription initiation complex. (A) Comprehensive mutagenesis of the LSP promoter. Run-off transcription assays were performed using synthetic LSP templates and human mtRNAP, TFB2M, and TFAM. (B, C) A close-up view of the active sites of human mtRNAP and T7 RNAP initiation complexes, PDB ID 6ERP and 1QLN. Conserved structural elements of the RNAPs – the G helix and the specificity loop-interact with the -3 and -4 bases of promoter DNA. Note that the residues in the proximity to -3 and -4 bases are shown as alanines in the SP loop of human IC. The position of the -5 base in the template strand of LSP is different from the -5 base in T7 RNAP IC because it has been artificially pre-melted. (D, E) Sequence alignment of the G helix (D) and the specificity loop (E) of mtRNAP in mammalian species. Residues that are identical or similar to human sequence are highlighted in yellow.