Association of phosphatidylinositol 3-kinase with nuclear transcription sites in higher plants

The kinases responsible for phosphorylation of inositol-containing lipids a re essential for many aspects of normal eukaryotic cell function. Genetic a nd biochemical studies have established that the phosphatidylinositol (PtdI ns) 3-kinase encoded by the yeast VPS34 gene is essential for the efficient sorting and delivery of proteins to the vacuole; the kinase encoded by the human VPS34 homolog has been equally implicated in the control of intracel lular vesicle traffic. The plant VPS34 homolog also is required for normal growth and development, and although a role for PtdIns 3-kinase in vesicle trafficking is likely, it has not been established. In this study, we have shown that considerable Ptdlns 3-kinase activity is associated with the int ernal matrix of nuclei isolated from carrot suspension cells. Immunocytoche mical and confocal laser scanning microscopy studies using the monoclonal a ntibody JIM135 (John Innes Monoclonal 135), raised against a truncated vers ion of the soybean Ptdlns 3-kinase, SP13K-5p, revealed that this kinase app ears to have a distinct and punctate distribution within the plant nucleus and nucleolus. Dual probing of root sections with JIM135 and anti-bromo-UTP antibodies, after in vitro transcription had been allowed to proceed in th e presence of bromo-UTP, showed that SP13K-5p associates with active nuclea r and nucleolar transcription sites. These findings suggest a possible link between PtdIns 3-kinase activity and nuclear transcription in plants.