Fig. 4: A proposed model for the helicase-polymerase coupling in the formation of SARS-CoV-2 RTC.
From: Architecture of a SARS-CoV-2 mini replication and transcription complex
Nsps composed mini RTC and template-primer RNAs are shown as schematic diagrams. Step 1, nsp12 bound nsp7, and nsp8 to constitute central RTC, waiting for a template RNA unwinding. The nsp13 molecule keeps in an inactive state. Step 2, an nsp13 (nsp13-1) contacts central RTC to form a platform to recruit the nsp13-2. Step 3, nsp13-2 is assembled into mini RTC, and contacts with nsp13-1, allowing the bound RNA translocating towards nsp12 activity center. Step 4, the unwinded single-strand RNA template passes through the RNA-binding channel of nsp13-2 and extends to nsp12 active center for the subsequent nascent RNA synthesis.
