plasmic splicing and represents the singular
example of extranuclear mRNA splicing in
eukaryotes. Ligation of the two exons is
mediated by the tRNA ligase Rlg1/Trl1 (tRNA
Ligase 1) that is also important to promote the
subsequent translation of the spliced HAC1
mRNA (Mori et al. 2010; Sidrauski et al. 1996)
and to produce the central transcriptional regulator of the UPR termed Hac1 in S. cerevisiae
(Homologous to ATF/CREB 1) and XBP1 (Xbox Binding Protein 1) in humans.
In contrast to the conserved Ire1 function,
the size of the unconventionally cleaved intron
shows increased variation in different fungi.
Experimentally validated unconventionally
spliced introns range in their size from 20 to
23 nucleotides (nt) in filamentous ascomycetes
(Hooks and Griffiths-Jones 2011) and from 56
to 65 nt in the basidiomycetes Cryptococcus
neoformans and Ustilago maydis. In S. cerevisiae the unconventional intron encompassing
252 nt mediates translation repression of the
unspliced HAC1 mRNA via base pairing with
the 5
0 untranslated region (UTR) of the mRNA.
Recent studies in Candida parapsilosis identified a 626 nt unconventional intron, the putaFig. 3.2 Unconventional splicing by Ire1. Activation of
Ire1 is mediated by direct binding of misfolded proteins to the ER luminal domain of Ire1 and by sequestration of Ire1-interacting Bip1 to misfolded proteins,
both of which promote Ire1 oligomerisation and transautophosphorylation. Activated Ire1 oligomers recognize the conserved twin stem-loop structures comprising the CNG’CNGN consensus sequence in the loop
regions of mRNAs encoding Hac1-like proteins. An
overview of experimentally validated intron sequences
in selected fungi is provided below. Sc Saccharomyces
cerevisiae, Tr Trichoderma reesei, Af Aspergillus fumigatus, Anig Aspergillus niger, Mo Magnaporthe oryzae,
Cn Cryptococcus neoformans, Nc Neurospora crassa,
Um Ustilago maydis, Cp Candida parapsilosis, Ca Candida albicans
52
R. Harting and K. Heimel
example of extranuclear mRNA splicing in
eukaryotes. Ligation of the two exons is
mediated by the tRNA ligase Rlg1/Trl1 (tRNA
Ligase 1) that is also important to promote the
subsequent translation of the spliced HAC1
mRNA (Mori et al. 2010; Sidrauski et al. 1996)
and to produce the central transcriptional regulator of the UPR termed Hac1 in S. cerevisiae
(Homologous to ATF/CREB 1) and XBP1 (Xbox Binding Protein 1) in humans.
In contrast to the conserved Ire1 function,
the size of the unconventionally cleaved intron
shows increased variation in different fungi.
Experimentally validated unconventionally
spliced introns range in their size from 20 to
23 nucleotides (nt) in filamentous ascomycetes
(Hooks and Griffiths-Jones 2011) and from 56
to 65 nt in the basidiomycetes Cryptococcus
neoformans and Ustilago maydis. In S. cerevisiae the unconventional intron encompassing
252 nt mediates translation repression of the
unspliced HAC1 mRNA via base pairing with
the 5
0 untranslated region (UTR) of the mRNA.
Recent studies in Candida parapsilosis identified a 626 nt unconventional intron, the putaFig. 3.2 Unconventional splicing by Ire1. Activation of
Ire1 is mediated by direct binding of misfolded proteins to the ER luminal domain of Ire1 and by sequestration of Ire1-interacting Bip1 to misfolded proteins,
both of which promote Ire1 oligomerisation and transautophosphorylation. Activated Ire1 oligomers recognize the conserved twin stem-loop structures comprising the CNG’CNGN consensus sequence in the loop
regions of mRNAs encoding Hac1-like proteins. An
overview of experimentally validated intron sequences
in selected fungi is provided below. Sc Saccharomyces
cerevisiae, Tr Trichoderma reesei, Af Aspergillus fumigatus, Anig Aspergillus niger, Mo Magnaporthe oryzae,
Cn Cryptococcus neoformans, Nc Neurospora crassa,
Um Ustilago maydis, Cp Candida parapsilosis, Ca Candida albicans
52
R. Harting and K. Heimel