L-chicoric acid (L-CA) is a potent inhibitor of HIV integrase (IN) in vitro. In this report, the effects of a glycine to serine mutation at position 140 (G140S) on HIV IN and its effects on IN inhibitor resistance are described. HIV containing the G140S mutation showed a delay in replication. Using real-time polymerase chain reaction, the delay was secondary to a failure in integration. The mutant protein (IN G 1 4 0 S ) was attenuated approximately four-fold for catalysis under equilibrium conditions compared to wild-type IN (IN W T ) and attenuated five-fold in steady-state kinetic analysis of disintegration. Fifty percent inhibitory concentration assays were performed with IN inhibitors against both IN proteins in disintegration and strand transfer reactions. IN G 1 4 0 S was resistant to both L-CA and L-731,988, a diketoacid. HIV containing the mutation was resistant to both inhibitors as well. The G140S mutation attenuates IN activity and confers resistance to IN inhibitors, suggesting that diketoacids and L-CA interact with a similar binding site on HIV IN.