SPATIAL ASSOCIATION OF HIV-1 TAT PROTEIN AND THE NUCLEOLAR TRANSPORT PROTEIN B23 IN STABLY TRANSFECTED JURKAT T-CELLS

The human immunodeficiency virus (HIV-1) encodes a transactivator prot ein, the product of the tat gene (tat), which is essential for virus r eplication In this study, immunogold electron microscopy was used in a stably transfected Jurkat T-cell line that constitutively expresses H IV-I tat protein to determine the subcellular and intranuclear distrib ution of tat protein. Two nucleocytoplasmic shuttle proteins C23/nucle olin and B23 and a third nucleolar antigen that was detected by monocl onal antibody MAb 1277 were also examined. In addition, spatial associ ation of C23 and B23 with tat protein at several subcellular locations was examined in dual-labeling experiments. The results showed that ta t protein was found in both the cytoplasm and nucleus but was especial ly prominent within the dense fibrillar and granular components of the nucleolus. There was little labeling of tat protein in the fibrillar centers where MAb 1277 antigen was localized at a comparatively high l evel. The subcellular and intranucleolar distribution of tat protein w as virtually identical to the pattern seen with C23 and B23. Although the intranuclear distributions of C23, B23 and tnt protein were very s imilar, C23 and tat protein were seldom spatially associated. In contr ast, B23 and tat protein were frequently spatially associated in the n ucleolus and in several other subcellular locations including the cyto plasm, nucleoplasm, at the nuclear envelope and plasma membrane. While a physical association was not directly demonstrated in this study, t he spatial association between B23 and tat protein strongly suggest th at such an association may exist.