INTRACELLULAR-DISTRIBUTION OF SMALL HEAT-STRESS PROTEINS IN CULTURED-CELLS OF LYCOPERSICON-PERUVIANUM

In view of the contradictory reports on the nuclear localization of sm all heat stress proteins (HSPs) we reinvestigated the situation in tom ato cell cultures using three different methods: protein analysis of h ighly purified nuclei, immunofluorescence with isolated nuclei and imm une electron microscopy. Results demonstrate the accumulation of HSP17 in tomato cell nuclei under different heat stress and recovery condit ions. The relative amount in nuclei parallels the synthesis and accumu lation of HSP17 in the cells. The distribution of HSP17 between nucleo li, nucleoplasm, cytoplasmic heat stress granules and cytoplasm change s in the course of heat stress and recovery. The spectrum of the isofo rms of the small HSPs is identical in whole cell extracts, purified nu clei and heat stress granules. Binding of HSP17 to the nucleolar preri bosomal material as well as to the cytoplasmic heat stress granules ma y indicate similar functions for protection of RNP material.