Identification of three major phosphorylation sites within HIV-1 capsid - Role of phosphorylation during the early steps of infection

We previously reported the presence of two cellular serine/threonine protei n kinases incorporated in human immunodeficiency virus type 1 (HIV-1) parti cles. One protein kinase is MAPK ERK2 (mitogen-activated protein kinase), w hereas the other one, a 53-kDa protein, still needs to be identified. Furth ermore, we demonstrated that the capsid protein CAp24 is phosphorylated by one of those two virion-associated protein kinases (Cartier, C., Deckert, M ., Grangeasse, C., Trauger, R., Jensen, F., Bernard, k, Cozzone, k, Desgran ges, C., and Boyer, V. (1997) J. Virol. 71, 4832-4837). In this study, we s howed that CAp24 is not a direct substrate of MAPK ERK2. Moreover, using si te-directed mutagenesis of each of the 9 serine residues of CAp24, we demon strated the phosphorylation of 3 serine residues (Ser-109, Ser-149, and Ser -178) in the CAp24. Substitution of each serine residue did not affect vira l budding, nor viral structure. By contrast, substitution of Ser-109, Ser-1 49, or Ser-178 affects viral infectivity by preventing the reverse transcri ption process to be completely achieved. Our results suggest that CAp24 ser ine phosphorylation is essential for viral uncoating process.