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Tetrahymena metallothioneins fall into two discrete subfamilies.

Díaz S, Amaro F, Rico D, Campos V, Benítez L, Martín-González A, Hamilton EP, Orias E, Gutiérrez JC - PLoS ONE (2007)

Bottom Line: We report the results of phylogenetic and gene expression analyses that include two new Tetrahymena thermophila metallothionein genes (MTT3 and MTT5).Conserved DNA motifs with potential regulatory significance were identified, in an unbiased way, upstream of the start codons of subfamily 7a MTs.EST evidence for alternative splicing in the 3' UTR of the MTT5 mRNA with potential regulatory activity is reported.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Microbiología-III, Facultad de Biología, Universidad Complutense (UCM), Spain.

ABSTRACT

Background: Metallothioneins are ubiquitous small, cysteine-rich, multifunctional proteins which can bind heavy metals.

Methodology/principal findings: We report the results of phylogenetic and gene expression analyses that include two new Tetrahymena thermophila metallothionein genes (MTT3 and MTT5). Sequence alignments of all known Tetrahymena metallothioneins have allowed us to rationalize the structure of these proteins. We now formally subdivide the known metallothioneins from the ciliate genus Tetrahymena into two well defined subfamilies, 7a and 7b, based on phylogenetic analysis, on the pattern of clustering of Cys residues, and on the pattern of inducibility by the heavy metals Cd and Cu. Sequence alignment also reveals a remarkably regular, conserved and hierarchical modular structure of all five subfamily 7a MTs, which include MTT3 and MTT5. The former has three modules, while the latter has only two. Induction levels of the three T. thermophila genes were determined using quantitative real time RT-PCR. Various stressors (including heavy metals) brought about dramatically different fold-inductions for each gene; MTT5 showed the highest fold-induction. Conserved DNA motifs with potential regulatory significance were identified, in an unbiased way, upstream of the start codons of subfamily 7a MTs. EST evidence for alternative splicing in the 3' UTR of the MTT5 mRNA with potential regulatory activity is reported.

Conclusion/significance: The small number and remarkably regular structure of Tetrahymena MTs, coupled with the experimental tractability of this model organism for studies of in vivo function, make it an attractive system for the experimental dissection of the roles, structure/function relationships, regulation of gene expression, and adaptive evolution of these proteins, as well as for the development of biotechnological applications for the environmental monitoring of toxic substances.

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Phylogenetic tree of 8 Tetrahymena MTs.The alignments shown in Fig 3 were used to construct the tree using Mr. Bayes (mixed protein model). The tree was rooted at its midpoint. The numbers represent the posterior probabilities that each branching is correct.
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pone-0000291-g004: Phylogenetic tree of 8 Tetrahymena MTs.The alignments shown in Fig 3 were used to construct the tree using Mr. Bayes (mixed protein model). The tree was rooted at its midpoint. The numbers represent the posterior probabilities that each branching is correct.

Mentions: A phylogenetic tree was constructed by submitting the alignment in Fig. 3 to the “Mr. Bayes” software ([32], using a “mixed protein” model). The tree (Fig. 4) reinforces the distinctions between the two groups identified above: the posterior probability that the two branches are correctly separated is 1.0. Ciliate MTs have been assigned to MT family 7 [33]. Based on this phylogenetic analysis, on the organization of cysteine clusters, and on the types of elementary building blocks assembled during the evolution of these proteins (see below), we define two subfamilies of Tetrahymena MTs. Subfamily 7a consists of T. thermophila MTT1, MTT3 and MTT5 and T. pyriformis MT-1 and MT-2. Subfamily 7b consists of T. thermophila MTT2 and MTT4, as well as T. pigmentosa MT-2.


Tetrahymena metallothioneins fall into two discrete subfamilies.

Díaz S, Amaro F, Rico D, Campos V, Benítez L, Martín-González A, Hamilton EP, Orias E, Gutiérrez JC - PLoS ONE (2007)

Phylogenetic tree of 8 Tetrahymena MTs.The alignments shown in Fig 3 were used to construct the tree using Mr. Bayes (mixed protein model). The tree was rooted at its midpoint. The numbers represent the posterior probabilities that each branching is correct.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC1808422&req=5

pone-0000291-g004: Phylogenetic tree of 8 Tetrahymena MTs.The alignments shown in Fig 3 were used to construct the tree using Mr. Bayes (mixed protein model). The tree was rooted at its midpoint. The numbers represent the posterior probabilities that each branching is correct.
Mentions: A phylogenetic tree was constructed by submitting the alignment in Fig. 3 to the “Mr. Bayes” software ([32], using a “mixed protein” model). The tree (Fig. 4) reinforces the distinctions between the two groups identified above: the posterior probability that the two branches are correctly separated is 1.0. Ciliate MTs have been assigned to MT family 7 [33]. Based on this phylogenetic analysis, on the organization of cysteine clusters, and on the types of elementary building blocks assembled during the evolution of these proteins (see below), we define two subfamilies of Tetrahymena MTs. Subfamily 7a consists of T. thermophila MTT1, MTT3 and MTT5 and T. pyriformis MT-1 and MT-2. Subfamily 7b consists of T. thermophila MTT2 and MTT4, as well as T. pigmentosa MT-2.

Bottom Line: We report the results of phylogenetic and gene expression analyses that include two new Tetrahymena thermophila metallothionein genes (MTT3 and MTT5).Conserved DNA motifs with potential regulatory significance were identified, in an unbiased way, upstream of the start codons of subfamily 7a MTs.EST evidence for alternative splicing in the 3' UTR of the MTT5 mRNA with potential regulatory activity is reported.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Microbiología-III, Facultad de Biología, Universidad Complutense (UCM), Spain.

ABSTRACT

Background: Metallothioneins are ubiquitous small, cysteine-rich, multifunctional proteins which can bind heavy metals.

Methodology/principal findings: We report the results of phylogenetic and gene expression analyses that include two new Tetrahymena thermophila metallothionein genes (MTT3 and MTT5). Sequence alignments of all known Tetrahymena metallothioneins have allowed us to rationalize the structure of these proteins. We now formally subdivide the known metallothioneins from the ciliate genus Tetrahymena into two well defined subfamilies, 7a and 7b, based on phylogenetic analysis, on the pattern of clustering of Cys residues, and on the pattern of inducibility by the heavy metals Cd and Cu. Sequence alignment also reveals a remarkably regular, conserved and hierarchical modular structure of all five subfamily 7a MTs, which include MTT3 and MTT5. The former has three modules, while the latter has only two. Induction levels of the three T. thermophila genes were determined using quantitative real time RT-PCR. Various stressors (including heavy metals) brought about dramatically different fold-inductions for each gene; MTT5 showed the highest fold-induction. Conserved DNA motifs with potential regulatory significance were identified, in an unbiased way, upstream of the start codons of subfamily 7a MTs. EST evidence for alternative splicing in the 3' UTR of the MTT5 mRNA with potential regulatory activity is reported.

Conclusion/significance: The small number and remarkably regular structure of Tetrahymena MTs, coupled with the experimental tractability of this model organism for studies of in vivo function, make it an attractive system for the experimental dissection of the roles, structure/function relationships, regulation of gene expression, and adaptive evolution of these proteins, as well as for the development of biotechnological applications for the environmental monitoring of toxic substances.

Show MeSH
Related in: MedlinePlus