Figure 2.

Alternative structures of the metamorphic polymerase domain. (A) The extended structure observed in the p66E subunit of RT; (B) the compact structure observed in the p51 subunit of the RT heterodimer. Color coding is: fingers (green); palm (blue); thumb (orange); connection (magenta). The position of the RH domain in the p66 subunit is also shown (brown), although this domain does not participate in the metamorphic rearrangement. The extended conformation includes a short, four-stranded β-sheet that forms part of the palm:connection interface in the extended conformation (boxed) that is not present in the compact conformation. Black arrows indicate the major domain rearrangements that need to occur for the metamorphic transition.