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An ortholog of farA of Aspergillus nidulans is implicated in the…
An ortholog of farA of Aspergillus nidulans is implicated in the transcriptional activation of genes involved in fatty acid utilization in the yeast Yarrowia lipolytica
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Discussion
Transcription of ALK1 - not activated by fatty acids in the wildtype cells
- slight increase in ALK1 transcript
was observed on oleic acid in the deletion mutant of POR1
- presence of inositol, PA is consumed for phosphatidylinositol synthesis, and Opi1p is released from the ER membrane and represses the transcription of target genes by binding to Ino2p in the nucleus
- Yas3p also localizes to ER in the presence of n-alkane and in the nucleus in the presence of n-alkane [8], and this raises the possibility that Yas3p binds to lipids or alkane metabolites in the ER membrane. The deletion of POR1 could cause an indirect effect on the amount of the potential ligand of Yas3p in the ER membrane and this resulted in transcriptional activation of ALK1.
- Yas1p, Yas2p, and Yas3p (orthologs of Ino4p, Ino2p, and Opi1p) involved in the transcriptional regulation of phospholipid biosynthetic genes in S. cerevisiae - transcriptional repressor Opi1p localizes to the ER membrane by binding to phosphatidic acid (PA) membrane protein Scs2p in the absence of inositol, and Ino2p and Ino4p activate the transcription of phospholipid synthetic genes
Characterized POR1
gene encoding the ortholog of farA encodes the transcription factor in:
- fatty acid metabolism
- peroxisomal function in A. nidulans
Deletion of POR1:
- severe growth defects on FA
Defects defects in the transcriptional induction of
genes involved in fatty acid utilization:
- by oleic acid were observed in the deletion mutant of POR1.
- results strongly imply that mutants of YALI0F13321g, YALI0D17988g, and/or YALI0D10681g exhibited low similarity to Oaf1p and/or Pip2p in their zinc cluster domains showed no significant defects on oleic acid
- less probable that orthologs of Oaf1p and/or Pip2p function in fatty acid response in Y. lipolytica
F. solani
expression of cutinase genes, cut1 and cut2, is differentially regulated by CTF1a and CTF1b. CTF1b participate in the constitutive expression of cut2
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It is plausible that unidentified functional homolog(s) may be involved in the transcriptional activation in response to fatty acid in Y. lipolytica
:check: it is possible that distinct regulatory mechanisms are involved in the fatty acid response
transcriptional activation of a subset of b-oxidation genes in the presence of oleic acid was observed in the deletion mutant of CTF1 in C. albicans
FarA and FarB bind to the CCTCGG (complement, CCGAGG)
- core element conserved in the promoter of thier target gene
- found at 127 to 122 in the 50 -non-coding regions of POT1, 120 to 115 of POX2, 221 to 216 of PEX5, and 55 to 50 of PAT1 of Y. lipolytica
- element in PAT1 promoter is located adjacent to its potential TATA box
- sequence CGAGCCGA consistent with the sequence in the palindrome 1 and 2 proposed as a binding site of CTF1a and CTF1b in the promoters of cutinase genes in F. solani
- found at 173 to 166 and 244 to 237 in the 50 -non-coding regions of PAT1 and POT1,
- functional significances of these elements remain to be
examined
Transcription of POT1, PAT1, POX2, and PEX5:
- induced by both oleic acid and n-decane
- Deletion of POR1 also affected transcript
levels of these genes on n-decane to varying extent
Y. lipolytica
- n-alkanes are oxidized to fatty acids
- then metabolized through b-oxidation
- transcription of these genes could in
part be activated by fatty acids produced in the process of oxidation of n-alkanes by the action of Por1p
considerable growth of the deletion mutant of POR1 on n-alkanes suggests:
- the expression of genes involved in b-oxidation and peroxisome proliferation is sufficient to support growth on n-alkanes even in the absence of Por1p.
- Partial activation of these genes by n-decane in the deletion mutant of POR1 could be mediated by Yas1p
and Yas2p through ARE1
ARE1-like sequences found:
- found at -207 to -171 in the 50 -non-coding region of POT1
- at 396 to 376 of PAT1
- in would be interest to analyze on n-alkanes in the double deletion mutant of POR1
and YAS1 or YAS2
Slight growth impairment of the Dpor1 strain
on n-decane
- due to the accumulation of harmful metabolites of n-decane caused by decrease in the expression of genes involved in fatty acid utilization
- northern blot analysis, the transcript level of PAT1 was not increased on n-decane in the deletion mutant of POR1 - significant increase in the bgalactosidase activity was observed on n-decane in the reporter assay using PAT1 promoter - Post-transcriptional regulation by carbon sources might be involved in fatty acid response in Y. lipolytica.
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