Human immunodeficiency virus type 1 has an additional coding sequence in the central region of the genome.

Eight coding regions designated gag, pol, env, sor, R, tat, art/trs, and 3' orf have been identified in the genome of the human immunodeficiency virus type 1 (HIV-1). Several other open reading frames have the potential to encode additional viral proteins. In this study, we show that HIV-1 has another coding sequence whose product is expressed during natural infection. Unlike antibody to other HIV-1 proteins, the prevalence of antibody to the product encoded by this region is elevated in patients with acquired immune deficiency syndrome (AIDS). Because no analogous coding region has been identified in HIV-2, the antibody to the product of this coding region may serve as a marker to distinguish infection with HIV-1 from infection with HIV-2.