Lys101Glu is a drug resistance mutation in reverse transcriptase clinically observed in HIV-1 from infected patients treated with the non-nucleoside inhibitor (NNRTI) drugs nevirapine and efavirenz. In contrast to many NNRTI resistance mutations, Lys101(p66 subunit) is positioned at the sur-face of the NNRTI pocket where it interacts across the reverse transcrip-tase (RT) subunit interface with Glu138(p51 subunit).