Cloning and Sequencing of Four New Metallothionein Genes from Tetrahymena thermophila and T. pigmentosa: Evolutionary Relationships in Tetrahymena MT Family

Cloning, characterization, and gene expression analysis of a novel cadmium metallothionein gene in Tetrahymena pigmentosa

“…The Tpig-MT1 gene is unusually long (521 bp), uses TGA as the stop codon, and is intronless. The deduced amino acid sequence of the protein reveals a high degree of internal similarity, as seen for other Tetrahymena MTs (Boldrin et al, 2003;Diaz et al, 2007).…”

“…Cd-MTs have been previously reported in T. pyriformis, T. pigmentosa, T. thermophila and T. tropicalis (Piccinni et al, 1994(Piccinni et al, , 1999Shang et al, 2002;Boldrin et al, 2003;Fu and Miao, 2006;Diaz et al, 2007, Shuja andShakoori, 2007). The Tpig-MT1 gene is unusually long (521 bp), uses TGA as the stop codon, and is intronless.…”

“…The previous report showed that MT1 in T. pyriformis contained two regions of internal similarity, MT1 (a) and MT1 (b), which have 50.8% identity (Piccinni et al, 1999;Boldrin et al, 2003). According to this criterion all reported Cd-MTs can be divided up into several parts, and multiple sequence alignments among each part of all reported Cd-MTs with Tpig-MT1 revealed that it also contains two similar regions.…”

“…According to their phylogenetic relationships, the pattern of clustering of Cys residues, and which metal inducer they preferentially respond to, they were grouped into Cd-MTs (subfamily 7a) or Cu-MTs (subfamily 7b), showing little sequence identity with one another. The Tetrahymena isoforms so far characterized show unusually longer peptide chains than almost all MTs reported in other organisms and showed only limited similarities with a unique internal homology (Boldrin et al, 2003;Diaz et al, 2007). Previous studies indicated that the two different Tetrahymena-MT polypeptides carry out different biological functions in the process of metal homeostasis and detoxification (Boldrin et al, 2002).…”

“…Different MT isoforms have been described in the unicellular ciliated protozoan genus Tetrahymena (T. pyriformis, T. pigmentosa, T. thermophila and T. tropicalis; Piccinni et al, 1999;Shang et al, 2002;Boldrin et al, 2003;Fu and Miao, 2006;Diaz et al, 2007, Shuja andShakoori, 2007). According to their phylogenetic relationships, the pattern of clustering of Cys residues, and which metal inducer they preferentially respond to, they were grouped into Cd-MTs (subfamily 7a) or Cu-MTs (subfamily 7b), showing little sequence identity with one another.…”