Maintenance of an unusual polypurine tract in HIV-2: stability to passage in culture.

A stretch of purine residues, the polypurine tract (PPT), is found in all retroviruses and is used to initiate plus-strand DNA synthesis. While the PPT of most lentiviruses is a homogeneous sequence of purine residues, the PPT of some isolates of the human and simian immunodeficiency viruses is interrupted with a single pyrimidine residue. The ROD strain of human immunodeficiency virus type 2 (HIV-2) has such a pyrimidine-containing variant PPT. Virus generated from an infectious molecular clone, pROD10, was used to infect two CD4-positive T-cell lines, H9 and CEM. The sequence of the PPT was determined after two passages. From both cell lines, the variant PPT was retained, demonstrating that the presence of a pyrimidine in the PPT was fully functional and that there was no strong selection for an all-purine PPT.