ELSEVIER Virus Research 39 (1995) 251-259 Virus Research Primary genetic characterization of HIV-1 isolates from WHO-sponsored vaccine evaluation sites by the RNase-A mismatch method S. S~nchez-Palomino a,2, j. Dopazo b, I. Olivares a, M.J. Martin c, C. L6pez-Gallndez a,. For the WHO Network for HIV Isolation and Characterization a Centro Nacional de Biologia Celular y Retrovirus, Instituto de Salud Carlos III, Majadahonda, Madrid 28220, Spain b Centro Nacional de Biotecnolog[a, CSIC, Universidad Aut6noma, Cantoblanco, 28049 Madrid, Spain c TDI, c / Condes de Torreanaz 5, 28028 Madrid, Spain Received 27 June 1995; revised 8 September 1995; accepted 9 September 1995 Abstract We have analyzed by the RNase-A mismatch method 35 isolates from four WHO-spon- sored vaccine evaluation sites as a secondary laboratory of the WHO Network for HIV Isolation and Characterization. The application of an estimator for the establishment of genetic distances based on the RNase-A digestion patterns in combination with the phylogenetic analysis has allowed us to construct a tree with five well defined groups of viruses. Because the clustering with known reference strains, samples from Brazil could be grouped as subtype B and the majority of those from Thailand were subtype E. Some of the samples from Uganda were classified as subtype D. Isolates from Rwanda and some from Uganda were identified as subtype A viruses. These results coincide with data obtained by heteroduplex mobility assay and nucleotide sequencing in env regions. The RNase-A mismatch method combined with phylogenetic analysis permitted the primary genetic classification of 33 of 35 samples from the WHO Network. Keywords: HIV isolate; RNase-A mismatch; World Health Organization; Vaccine evalua- tion * Corresponding author. Fax: (341) 638 82 06. l Present address: Centro de Biologia Molecular 'Severo Ochoa', Universidad Aut6noma, Canto- blanco, 28049 Madrid, Spain. 0168-1702/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0168-1702(95)00096-8