X-ray structure of HIV-1 reverse transcriptase in complex with primer–template DNA and dATP. (a) A ribbon diagram of the p66 subunit in which the N-terminal fingers domain is blue, the palm is red, the thumb is green, the connection is yellow, and the RNase H domain is magenta. (b) The p51 subunit colored as is p66 (but missing the RNase H domain) and with its palm domain oriented similarly to that of p66. Note the different orientations of its other three domains relative to those of p66. (c) A ribbon diagram of the HIV-1 RT p66/p51 heterodimer in complex with DNA and dATP. The domains of p66 and p51 are colored as in Parts a and b. The DNA is drawn in paddle form in orange with its 5' nucleotides red. The dATP is drawn in space-filling form with C gray, N blue, O red, and P orange. The complex is initially oriented with its p66 polymerase subunit toward the top of the figure and viewed toward the protein's template–primer binding cleft (whose floor is largely composed of the connection domains of p66 and p51). [Based on an X-ray structure by Edward Arnold, Rutgers University. PDBid 3JYT.]