Abstract
Phytochelatins (PCs), a family of heavy metal-inducible peptides important in the detoxification of heavy metals, have been identified in plants and some microorganisms, including Schizosaccharomyces pombe, but not in animals. PCs are synthesized enzymatically from glutathione (GSH) by PC synthase in the presence of heavy metal ions. In Arabidopsis, the CAD1 gene, identified by using Cd-sensitive, PC-deficient cad1 mutants, has been proposed to encode PC synthase. Using a positional cloning strategy, we have isolated the CAD1 gene. Database searches identified a homologous gene in S. pombe, and a mutant with a targeted deletion of this gene was also Cd sensitive and PC deficient. Extracts of Escherichia coli cells expressing a CAD1 cDNA or the S. pombe gene catalyzing GSH-dependent, heavy metal-activated synthesis of PCs in vitro demonstrated that both genes encode PC synthase activity. Both enzymes were activated by a range of metal ions. In contrast, reverse transcription-polymerase chain reaction experiments showed that expression of the CAD1 mRNA is not influenced by the presence of Cd. A comparison of the two predicted amino acid sequences revealed a highly conserved N-terminal region, which is presumed to be the catalytic domain, and a variable C-terminal region containing multiple Cys residues, which is proposed to be involved in activation of the enzyme by metal ions. Interestingly, a similar gene was identified in the nematode, Caenorhabditis elegans, suggesting that PCs may also be expressed in some animal species.
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Claims 9
Claim · model-written summary
CAD1 was isolated by positional cloning.
- Taxon
- Arabidopsis
Arabidopsist0 - Gene
- CAD1e0
- Outcome
- isolated the CAD1 genee0
Not reportedComparatorValue
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Using a positional cloning strategy, we have isolated the CAD1 gene.”
t0“Arabidopsis”
Claim · model-written summary
A homologous gene was identified in S. pombe.
- Taxon
- ArabidopsisArabidopsist0
- Gene
- homologous genee0
- Outcome
- homologous gene in S. pombee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Database searches identified a homologous gene in S. pombe, and a mutant with a targeted deletion of this gene was also Cd sensitive and PC deficient.”
t0“Arabidopsis”
Claim · model-written summary
Deletion of the S. pombe homolog caused Cd sensitivity and PC deficiency.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- targeted deletion of this genee0
- Gene
- this genee0
- Outcome
- Cd sensitive and PC deficiente0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a mutant with a targeted deletion of this gene was also Cd sensitive and PC deficient.”
t0“Arabidopsis”
Claim · model-written summary
Expression extracts showed CAD1 and the S. pombe homolog encode phytochelatin synthase activity.
- Taxon
- ArabidopsisArabidopsist0
- Gene
- CAD1e0
- Outcome
- PC synthase activitye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Extracts of Escherichia coli cells expressing a CAD1 cDNA or the S. pombe gene catalyzing GSH-dependent, heavy metal-activated synthesis of PCs in vitro demonstrated that both genes encode PC synthase activity.”
t0“Arabidopsis”
Claim · model-written summary
A range of metal ions activated both enzymes.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- a range of metal ionse0
- Outcome
- enzymese0
- Direction
- activatede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Both enzymes were activated by a range of metal ions.”
t0“Arabidopsis”
Claim · model-written summary
Cd did not influence CAD1 mRNA expression.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- Cde0
- Gene
- CAD1e0
- Outcome
- expression of the CAD1 mRNAe0
- Direction
- not influencede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“expression of the CAD1 mRNA is not influenced by the presence of Cd.”
t0“Arabidopsis”
Claim · model-written summary
The predicted proteins share a conserved N-terminal region.
- Taxon
- ArabidopsisArabidopsist0
- Outcome
- highly conserved N-terminal regione0
- Qualifier
- presumed to be the catalytic domaine0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A comparison of the two predicted amino acid sequences revealed a highly conserved N-terminal region, which is presumed to be the catalytic domain, and a variable C-terminal region containing multiple Cys residues, which is proposed to be involved in activation of the enzyme by metal ions.”
t0“Arabidopsis”
Claim · model-written summary
Their C-terminal regions vary and contain multiple cysteine residues.
- Taxon
- ArabidopsisArabidopsist0
- Outcome
- variable C-terminal region containing multiple Cys residuese0
- Qualifier
- proposed to be involved in activation of the enzyme by metal ionse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a variable C-terminal region containing multiple Cys residues, which is proposed to be involved in activation of the enzyme by metal ions.”
t0“Arabidopsis”
Claim · model-written summary
A similar gene was identified in C. elegans.
- Taxon
- ArabidopsisArabidopsist0
- Outcome
- similar gene was identified in the nematode, Caenorhabditis eleganse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a similar gene was identified in the nematode, Caenorhabditis elegans, suggesting that PCs may also be expressed in some animal species.”
t0“Arabidopsis”
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