title: Tobacco class I cytosolic small heat shock proteins are under transcriptional and translational regulations in expression and heterocomplex prevails under the high-temperature stress condition in vitro.
abstract: Seven genomic clones of tobacco (Nicotiana tabacum W38) cytosolic class I small heat shock proteins (sHSPs), probably representing all members in the class, were isolated and found to have 66 to 92% homology between their nucleotide sequences. Even though all seven sHSP genes showed heat shock-responsive accumulation of their transcripts and proteins, each member showed discrepancies in abundance and timing of expression upon high-temperature stress. This was mainly the result of transcriptional regulation during mild stress conditions and transcriptional and translational regulation during strong stress conditions. Open reading frames (ORFs) of these genomic clones were expressed in Escherichia coli and the sHSPs were purified from E. coli. The purified tobacco sHSPs rendered citrate synthase and luciferase soluble under high temperatures. At room temperature, non-denaturing pore exclusion polyacrylamide gel electrophoresis on three sHSPs demonstrated that the sHSPs spontaneously formed homo-oligomeric complexes of 200 ∼ 240 kDa. However, under elevated temperatures, hetero-oligomeric complexes between the sHSPs gradually prevailed. Atomic force microscopy showed that the hetero-oligomer of NtHSP18.2/NtHSP18.3 formed a stable oligomeric particle similar to that of the NtHSP18.2 homo-oligomer. These hetero-oligomers positively influenced the revival of thermally inactivated luciferase. Amino acid residues mainly in the N-terminus are suggested for the exchange of the component sHSPs and the formation of dominant hetero-oligomers under high temperatures.
authors.affiliation: School of Biological Sciences and Institute of Molecular Biology and Genetics, Seoul National University, Seoul, 151-742, Korea.
authors.forename: Soo Min
authors.initials: SM
authors.lastname: Park
authors.forename: Keun Pill
authors.initials: KP
authors.lastname: Kim
authors.forename: Myung Kuk
authors.initials: MK
authors.lastname: Joe
authors.forename: Mi Ok
authors.initials: MO
authors.lastname: Lee
authors.forename: Hyun Jo
authors.initials: HJ
authors.lastname: Koo
authors.forename: Choo Bong
authors.initials: CB
authors.lastname: Hong
mesh_terms: D000595:Amino Acid Sequence; D003600:Cytosol / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D015723:Gene Library; D017930:Genes, Reporter; D050888:Heat-Shock Proteins, Small / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D018869:Heat-Shock Response; D006358:Hot Temperature; D018832:Molecular Chaperones / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes; D010940:Plant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D016415:Sequence Alignment; D013696:Temperature; D014026:Nicotiana / Q000235:genetics / Q000502:physiology*
chemical_list: D050888:Heat-Shock Proteins, Small; D018832:Molecular Chaperones; D046912:Multiprotein Complexes; D010940:Plant Proteins
keywords: family member; molecular chaperone; post-transcriptional differentiation; temperature dependence; transcriptional differentiation