These models are custom depictions of the SARS-CoV-2 nsp12-nsp7-nsp8 complex bound to RNA template and primer, and the activated form of the drug remdesivir. nsp12 contains the RNA dependent RNA polymerase activity, and nsp7 and nsp8 are auxilliary proteins in the RNA-replication complex.  

 

nsp12 is blue, nsp7 is red and nsp8 is yellow. The RNA template strand is orange, and the RNA primer strand, which is being extended by the polymerase, is green. Remdesivir is shown as atoms that are colored by element.  Magnesium atoms in the binding pocket are the larger spheres.

 

Remdesivir is an RNA nucleotide analog, and works by getting inserted into the replicating RNA chain by the polymerase and disrupting the genetic information. It's position in the active site corresponds to the next nucleotide to be added to the newly synthesized chain, and this can be observed by how it stacks on the adjacent RNA monomer in the green strand that is being synthesized.

 

The ribbon model omits nsp7 and nsp8 for clarity, and shows the RNA strands as surfaces for contrast from the nsp12 protein.

The surface model also shows the section of the nsp12 binding pocket that is close to remdesivir in darker blue.