ART4 and infection: Ledgf-null mouse embryo fibroblasts (MEFs) transfected with a human LEDGF expression vector or its mutant forms were infected with single-round, vesicular stomatitis virus glycoprotein G (VSV-G)-pseudotyped HIV-1 vectors expressing a luciferase reporter gene (HIV-Luc), and the levels of luciferase activity in cell extracts were measured 44 h post infection.