Abstract
Maize heat shock protein of 101 KDa (HSP101) is essential for thermotolerance induction in this plant. The mRNA encoding this protein harbors an IRES element in the 5′UTR that mediates cap-independent translation initiation. In the current work it is demonstrated that hsp101 IRES comprises the entire 5′UTR sequence (150 nts), since deletion of 17 nucleotides from the 5′ end decreased translation efficiency by 87% compared to the control sequence. RNA structure analysis of maize hsp101 IRES revealed the presence of three stem-loops toward its 5′ end, whereas the remainder sequence contains a great proportion of unpaired nucleotides. Furthermore, HSP90 protein was identified by mass spectrometry as the protein preferentially associated with the maize hsp101 IRES. In addition, it has been found that eIFiso4G rather than eIF4G initiation factor mediates translation of the maize hsp101 mRNA.
Highlights
Maize heat shock protein of 101 kDa (HSP101) mRNA encodes a chaperone essential for thermo-tolerance induction in maize (Zea mays L.) [1]
We have previously shown that this mRNA harbors an Internal Ribosome Entry Site (IRES) element on its 59 untranslated region (59UTR) which mediates cap-independent translation initiation in cell free lysates [2]
The pBIC-5 construct, containing an active maize hsp101 IRES [2], harbors 60 nts belonging to the genomic region upstream of the transcription start site (+1) (Figure 1a)
Summary
Maize heat shock protein of 101 kDa (HSP101) mRNA encodes a chaperone essential for thermo-tolerance induction in maize (Zea mays L.) [1]. We have previously shown that this mRNA harbors an Internal Ribosome Entry Site (IRES) element on its 59 untranslated region (59UTR) which mediates cap-independent translation initiation in cell free lysates [2]. Capdependent translation was inhibited through the proteolysis of eIF4G induced by the action of the Lb protease. Most eukaryotic mRNAs contain a cap structure (m7GpppN, where N represents any nucleotide) at its 59UTR end. The cap structure is recognized by the eIF4F initiation factor consisting of eIF4A, eIF4G and eIF4E [3]. The eIF4E protein binds directly to the cap structure of the mRNA. It is essential for capdependent translation initiation and recruitment of the translational machinery
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