title: Complexity of Hsp90 in organelle targeting.
abstract: Heat shock protein 90 (Hsp90) is an abundant and highly conserved molecular chaperone. In Arabidopsis, the Hsp90 gene family consists of seven members. Here, we report that the AtHsp90-6 gene gives rise to two mRNA populations, termed AtHsp90-6L and AtHsp90-6S due to alternative initiation of transcription. The AtHsp90-6L and AtHsp90-6S transcription start sites are located 228 nucleotides upstream and 124 nucleotides downstream of the annotated translation start site, respectively. Both transcripts are detected under normal or heat-shock conditions. The inducibility of AtHsp90-6 mRNAs by heat shock implies a potential role of both isoforms in stress management. Stable transformation experiments with fusion constructs between the N-terminal part of each AtHsp90-6 isoform and green fluorescent protein indicated import of both fusion proteins into mitochondria. In planta investigation confirmed that fusion of the AtHsp90-5 N-terminus to green fluorescent protein (GFP) did result in specific chloroplastic localization. The mechanisms of regulation for mitochondria- and plastid-localized chaperone-encoding genes are not well understood. Future work is needed to address the possible roles of harsh environmental conditions and developmental processes on fine-tuning and compartmentalization of the AtHsp90-6L, AtHsp90-6S, and AtHsp90-5 proteins in Arabidopsis.
authors: Laboratory of Molecular Biology, Agricultural Biotechnology Department, Agricultural University of Athens, Athens, Greece.
authors: Constantinos
authors: C
authors: Prassinos
authors: Kosmas
authors: K
authors: Haralampidis
authors: Dimitra
authors: D
authors: Milioni
authors: Despina
authors: D
authors: Samakovli
authors: Konstantinos
authors: K
authors: Krambis
authors: Polydefkis
authors: P
authors: Hatzopoulos
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000378:metabolism; D001483:Base Sequence; D017931:DNA Primers; D018841:HSP90 Heat-Shock Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D015388:Organelles / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic
chemical_list: D017931:DNA Primers; D018841:HSP90 Heat-Shock Proteins; D012333:RNA, Messenger