NUCLEAR LOCATION OF A DIADENOSINE 5',5'''-P-1,P-4-TETRAPHOSPHATE (AP(4)A) HYDROLASE IN TOMATO CELLS GROWN IN SUSPENSION-CULTURES

Diadenosine 5',5'''-P-1,P-4-tetraphosphate (Ap(4)A) cleaving enzymes a re assumed to regulate intracellular levels of Ap(4)A, a compound know n to affect cell proliferation and stress responses. From plants an Ap (4)A hydrolase was recently purified using tomato cells grown in suspe nsion. It was partially sequenced and a peptide antibody was prepared (Feussner et al., 1996). Using this polyclonal monospecific antibody, an abundant nuclear location of Ap(4)A hydrolase in 4-day-old cells of a tomato cell suspension culture is demonstrated here by means of imm unocytochemical techniques using FITC (fluorescein-5-isothiocyanate) l abeled secondary antibodies. The microscopic analysis of the occurrenc e of Ap(4)A hydrolase performed for different stages of the cell cycle visualized by parallel DAPI (4,6-diamidino-2-phenylindole) staining r evealed that the protein accumulates within nuclei of cells in the int erphase, but is absent in the nucleus as well as cytoplasm during all stages of mitosis. This first intracellular localization of an Ap(4)A degrading enzyme within the nucleus and its pattern of appearance duri ng the cell cycle is discussed in relation to the suggested role of Ap (4)A in triggering DNA synthesis and cell proliferation.