MYRISTOYLATED AND NON-MYRISTOYLATED FORMS OF THE PH SENSOR PROTEIN HISACTOPHILIN-II - INTRACELLULAR SHUTTLING TO PLASMA-MEMBRANE AND NUCLEUS MONITORED IN REAL-TIME BY A FUSION WITH GREEN FLUORESCENT PROTEIN

Hisactophilins are myristoylated proteins that are rich in histidine r esidues and known to exist in Dictyostelium cells in a plasma membrane -bound and a soluble cytoplasmic state, Intracellular translocation of these proteins in response to pH changes was monitored using hisactop hilin fusions with green fluorescent protein (GFP) and confocal laser scanning microscopy, Both the normal and a mutated non-myristoylated f usion protein shuttled within the cells in a pH-dependent manner, Afte r lowering the pH, these proteins translocated within minutes between the cytoplasm, the plasma membrane and the nucleus. The role of histid ine clusters on the surface of hisactophilin molecules in binding of t he proteins to the plasma membrane and in their transfer to the nucleu s is discussed on the basis of a pH switch mechanism.