title: Cap-independent translation of maize Hsp101.
abstract: Maize embryonic axes contain stored mRNAs, some of which are able to undergo cap-independent translation initiation during germination. The Hsp101 mRNA, encoding a heat shock protein, is essential for thermo-tolerance induction and is present among the stored transcripts. This research aimed to investigate whether the Hsp101 transcript is IRES-driven regulated upon heat stress. Hsp101 transcribed either in vitro or in vivo was efficiently translated via a cap-independent mechanism. This was observed either in an animal in vitro translation system containing proteolytically cleaved eukaryotic initiation factor eIF4G or in a plant system lacking both eIF4E and eIFiso4E initiation factors. Deletion of the 5' untranslated region (UTR) from the Hsp101 mRNA abolished its cap-independent translation indicating that this nucleotide sequence is required to confer cap-independent initiation. Bicistronic constructs containing the Hsp101 mRNA 5'UTR in sense and anti-sense directions between two reporter genes were translated in both cap-independent systems. A similar bicistronic construct containing a viral internal ribosome entry site (IRES) element between the reporter genes was used as control. Internal translation of the second reporter gene was observed when the Hsp101 5'UTR was in the sense but not in the anti-sense orientation in the bicistronic construct. Taken together, these data suggest that the 5'UTR of maize Hsp101, a plant cellular mRNA, functions as an IRES-like element accounting for its cap-independent translation during heat stress.
authors.affiliation: Departamento de Bioquímica, Facultad de Química, Universidad Nacional Autónoma de México, 04510, México DF.
authors.forename: Tzvetanka D
authors.initials: TD
authors.lastname: Dinkova
authors.forename: Hilda
authors.initials: H
authors.lastname: Zepeda
authors.forename: Encarnación
authors.initials: E
authors.lastname: Martínez-Salas
authors.forename: Luz María
authors.initials: LM
authors.lastname: Martínez
authors.forename: Jorge
authors.initials: J
authors.lastname: Nieto-Sotelo
authors.forename: Estela Sánchez
authors.initials: ES
authors.lastname: de Jiménez
mesh_terms: D001483:Base Sequence; D003001:Cloning, Molecular; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000235:genetics*; D018514:Plant Structures / Q000235:genetics / Q000378:metabolism; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics; D018749:RNA, Plant / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics*; D003313:Zea mays / Q000235:genetics* / Q000378:metabolism
chemical_list: C115569:HSP101 protein, plant; D010940:Plant Proteins; D012333:RNA, Messenger; D018749:RNA, Plant; D014157:Transcription Factors