RT Journal Article
SR Electronic
T1 The Tomato Hsf System: HsfA2 Needs Interaction with HsfA1 for Efficient Nuclear Import and May Be Localized in Cytoplasmic Heat Stress Granules
JF Molecular and Cellular Biology
JO Mol. Cell. Biol.
FD American Society for Microbiology
SP 2240
OP 2251
DO 10.1128/MCB.18.4.2240
VO 18
IS 4
A1 Scharf, Klaus-Dieter
A1 Heider, Harald
A1 Höhfeld, Ingo
A1 Lyck, Ruth
A1 Schmidt, Enrico
A1 Nover, Lutz
YR 1998
UL http://mcb.asm.org/content/18/4/2240.abstract
AB In heat-stressed (HS) tomato (Lycopersicon peruvianum) cell cultures, the constitutively expressed HS transcription factor HsfA1 is complemented by two HS-inducible forms, HsfA2 and HsfB1. Because of its stability, HsfA2 accumulates to fairly high levels in the course of a prolonged HS and recovery regimen. Using immunofluorescence and cell fractionation experiments, we identified three states of HsfA2: (i) a soluble, cytoplasmic form in preinduced cultures maintained at 25°C, (ii) a salt-resistant, nuclear form found in HS cells, and (iii) a stored form of HsfA2 in cytoplasmic HS granules. The efficient nuclear transport of HsfA2 evidently requires interaction with HsfA1. When expressed in tobacco protoplasts by use of a transient-expression system, HsfA2 is mainly retained in the cytoplasm unless it is coexpressed with HsfA1. The essential parts for the interaction and nuclear cotransport of the two Hsfs are the homologous oligomerization domain (HR-A/B region of the A-type Hsfs) and functional nuclear localization signal motifs of both partners. Direct physical interaction of the two Hsfs with formation of relatively stabile hetero-oligomers was shown by a two-hybrid test inSaccharomyces cerevisiae as well as by coimmunoprecipitation using tomato and tobacco whole-cell lysates.