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. Author manuscript; available in PMC: 2018 Nov 16.
Published in final edited form as: Cell. 2017 Oct 12;171(5):1082–1093.e13. doi: 10.1016/j.cell.2017.09.035

Figure 6. Mechanism of transcription termination at CSBII.

Figure 6

(A) Schematics of the RNA transcript encoded in the CSBII region in human mitochondria. The G-quadruplex region (G6AG8 variant) is highlighted in red, the points of termination are indicated by asterisks.

(B) Schematic depiction of a possible RNA G-quadruplex structure having a single nucleotide bulge.

(C) The spacer region of CSBII is dispensable for termination of transcription. Transcription assays were performed using promoter templates with the WT and mutated CSBII sequence, in which the spacer region was deleted.

(D) The U-run encoded in the CSBII region is required for transcription termination. The transcription assay was performed using the WT and modified CSBII sequence (GC≫AT), in which the AT-rich sequence proximal to the termination site was substituted to the GC-rich sequence.

(E) RNA G-quadruplex structure clashes with the specificity loop and intercalating loop of mtRNAP. The model is obtained by extending the RNA in mtRNAP EC with the 16 nucleotide-long G-quadruplex (PDB ID 2M4P). The G-quadruplex (red) is shown formed in vicinity of the trailing edge of transcription bubble in EC (surface representation). The specificity loop is modeled based on TEFM-mtRNAP Bpa cross-linking data.

(F) Structure of the anti-termination complex (surface representation). Coloring as in Figure 4A. See also Figure S7