HUMAN-IMMUNODEFICIENCY-VIRUS MATRIX TYROSINE PHOSPHORYLATION - CHARACTERIZATION OF THE KINASE AND ITS SUBSTRATE REQUIREMENTS

During virus assembly, a subset of human immunodeficiency virus (HIV) matrix (MA) molecules is phosphorylated on C-terminal tyrosine. This m odification facilitates infection of nondividing cells by allowing for the recruitment of the karyophilic MA into the viral core and preinte gration complex, MA tyrosine phosphorylation is accomplished by a cell ular protein kinase which is incorporated into virions, In this study, we have investigated the nature of this enzyme as well as the determi nants of MA necessary for its phosphorylation, Employing an in vitro k inase assay, we found that the MA tyrosine kinase activity is present in various cultured cell lines including CEM and SupT1 T-lymphoid cell s, Namalwa B cells, 293 and CV-1 kidney fibroblasts, and P4 HeLa cells , In addition, it could be detected in platelets, macrophages, and act ivated peripheral blood lymphocytes (PBLs) but not in erythrocytes and resting PBLs isolated from human blood, Subcellular localization of t he kinase activity by cell fractionation demonstrated that it is enric hed in cellular membranes, In HN type 2 (HIV-2) particles, the MA tyro sine kinase is associated with the inner leaflet of the viral membrane , while the tyrosine-phosphorylated MA is localized to the core. Indiv idual mutations of each of the last eight residues immediately upstrea m of the C-terminal tyrosine (Y132) of HIV-1 MA did not prevent Y132 p hosphorylation, suggesting that the kinase does not require a highly s pecific sequence adjacent to the C-terminal tyrosine, Confirming this, we found that the MA of murine leukemia virus, the sequence of which is only moderately homologous to that of HIV-1 and HIV-2 MA, is also C -terminally tyrosine phosphorylated.