Characterization of a maize heat-shock protein 101 gene, HSP101, encoding a ClpB/Hsp100 protein homologue

Heat shock protein 101 (HSP101) cDNA and genomic clones from maize have been isolated. The structure of maize HSP101 reveals the presence of six exons interrupted by five introns. Maize HSP101 contains a predicted open reading frame that translates into a 912-aa sequence with a mass of 101kDa. Initiation of transcription was mapped 146 bases upstream of the AUG codon. Five heat shock element (HSE) boxes were found within the proximal 289 bases of the promoter region. Southern blot analysis of genomic DNA indicates that the maize genome contains only one copy of HSP101. A protein sequence comparison showed that maize Hsp101 belongs to the heat shock 100kDa and caseino-lytic protease B protein family (Hsp100/ClpB) that plays important roles in bacteria and yeast in the survival to extremely high temperatures and the control of proteolysis. Accumulation of HSP101 mRNA was strong under heat shock conditions, but not detectable after cold or osmotic stress treatments or by exogenous application of ABA. The analysis of the predicted supersecondary structure of maize Hsp101 showed that a coiled-coil located in the middle region of the protein is evolutionarily conserved in all members of the Clp A, B and C subfamilies. It is proposed that these supersecondary structures may have important roles in Clp function.