Complexity of Hsp90 in organelle targeting.
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.
Prassinos
Constantinos
C
Laboratory of Molecular Biology, Agricultural Biotechnology Department, Agricultural University of Athens, Athens, Greece.
Haralampidis
Kosmas
K
Milioni
Dimitra
D
Samakovli
Despina
D
Krambis
Konstantinos
K
Hatzopoulos
Polydefkis
P
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
D017931:DNA Primers; D018841:HSP90 Heat-Shock Proteins; D012333:RNA, Messenger