A3G, an innate restriction factor that inhibits human immunodeficiency virus-1 (HIV-1) infection, is a cytidine deaminase that catalyzes the deamination of cytosine to uracil in the single-stranded DNA substrate and restricts retroviral replication by inducing hypermutation in viral nascent reverse transcripts [20]. The gene discussed is APOBEC3G; the disease is HIV-1 infection.