Activation mechanisms of the HAC1-mediated unfolded protein response in filamentous fungi.
The unfolded protein response (UPR) is a regulatory pathway activating genes involved in multiple functions related to folding, quality control and transport of secreted proteins. Characterization of the hac1/hacA genes encoding the UPR transcription factors from the filamentous fungi Trichoderma reesei and Aspergillus nidulans is described in this article. The corresponding gene in Saccharomyces cerevisiae is activated through a non-spliceosomal intron-splicing reaction. The T. reesei hac1 and A. nidulans hacA mRNAs undergo an analogous splicing reaction of a 20-nt-long intron during UPR induction. This splicing changes the reading frame of the mRNA and thus could bring in an activation domain to the HACI/HACA proteins. In addition to the non-spliceosomal splicing, the hac1/A mRNAs of the filamentous fungi are truncated at the 5'-flanking region upon UPR induction. An upstream open reading frame is omitted from the mRNAs due to the truncation, and evidence is presented showing that the truncated T. reesei hac1 mRNA is translated more efficiently than a full-length mRNA. This paper reports a novel combination of two different regulatory mechanisms of a transcription factor gene, both operational at the mRNA level.
Saloheimo
Markku
M
VTT Biotechnology, 02044 VTT, Finland. Markku.Saloheimo@vtt.fi
Valkonen
Mari
M
Penttilä
Merja
M
D000595:Amino Acid Sequence; D001233:Aspergillus nidulans / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D050976:Basic-Leucine Zipper Transcription Factors; D004271:DNA, Fungal / Q000235:genetics; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005800:Genes, Fungal; D005816:Genetic Complementation Test; D007438:Introns; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D011401:Promoter Regions, Genetic; D017510:Protein Folding; D012323:RNA Processing, Post-Transcriptional; D012326:RNA Splicing; D012331:RNA, Fungal / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014242:Trichoderma / Q000235:genetics / Q000378:metabolism*
D050976:Basic-Leucine Zipper Transcription Factors; D004271:DNA, Fungal; D005656:Fungal Proteins; C091341:HAC1 protein, S cerevisiae; D012331:RNA, Fungal; D012333:RNA, Messenger; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors