Nuclear targeting of the beta isoform of type II phosphatidylinositol phosphate kinase (phosphatidylinositol 5-phosphate 4-kinase) by its alpha-helix 7.
Type II phosphatidylinositol phosphate kinases (PIPkins) have recently been found to be primarily phosphatidylinositol 5-phosphate 4-kinases, and their physiological role remains unclear. We have previously shown that a Type II PIPkin [isoform(s) unknown], is localized partly in the nucleus [Divecha, Rhee, Letcher and Irvine (1993) Biochem. J. 289, 617-620], and here we show, by transfection of HeLa cells with green-fluorescent-protein-tagged Type II PIPkins, that this is likely to be the Type IIbeta isoform. Type IIbeta PIPkin has no obvious nuclear localization sequence, and a detailed analysis of the localization of chimaeras and mutants of the alpha (cytosolic) and beta PIPkins shows that the nuclear localization requires the presence of a 17-amino-acid length of alpha-helix (alpha-helix 7) that is specific to the beta isoform, and that this helix must be present in its entirety, with a precise orientation. This resembles the nuclear targeting of the HIV protein Vpr, and Type IIbeta PIPkin is apparently therefore the first example of a eukaryotic protein that uses the same mechanism.
Ciruela
A
A
Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QJ, U.K.
Hinchliffe
K A
KA
Divecha
N
N
Irvine
R F
RF
D000595:Amino Acid Sequence; D002467:Cell Nucleus / Q000201:enzymology*; D049452:Green Fluorescent Proteins; D006367:HeLa Cells; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism*; D008164:Luminescent Proteins / Q000378:metabolism; D015778:Minor Histocompatibility Antigens; D008969:Molecular Sequence Data; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000737:chemistry / Q000378:metabolism*; D017433:Protein Structure, Secondary; D017386:Sequence Homology, Amino Acid
D007527:Isoenzymes; D008164:Luminescent Proteins; D015778:Minor Histocompatibility Antigens; D049452:Green Fluorescent Proteins; D017853:Phosphotransferases (Alcohol Group Acceptor); C402182:phosphatidylinositol phosphate 4-kinase