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The iron-sulfur cluster assembly genes iscS and iscU of Entamoeba histolytica were acquired by horizontal gene transfer.

van der Giezen M, Cox S, Tovar J - BMC Evol. Biol. (2004)

Bottom Line: E. histolytica IscU and IscS were found to contain all features considered essential for their biological activity, including amino acid residues involved in substrate and/or co-factor binding.The bacterial-type FeS cluster assembly genes of E. histolytica suggest their lateral acquisition from epsilon proteobacteria.This is a clear example of horizontal gene transfer (HGT) from eubacteria to unicellular eukaryotic organisms, a phenomenon known to contribute significantly to the evolution of eukaryotic genomes.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Biological Sciences, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK. mark.vandergiezen@rhul.ac.uk

ABSTRACT

Background: Iron-sulfur (FeS) proteins are present in all living organisms and play important roles in electron transport and metalloenzyme catalysis. The maturation of FeS proteins in eukaryotes is an essential function of mitochondria, but little is known about this process in amitochondriate eukaryotes. Here we report on the identification and analysis of two genes encoding critical FeS cluster (Isc) biosynthetic proteins from the amitochondriate human pathogen Entamoeba histolytica.

Results: E. histolytica IscU and IscS were found to contain all features considered essential for their biological activity, including amino acid residues involved in substrate and/or co-factor binding. The IscU protein differs significantly from other eukaryotic homologs and resembles the long type isoforms encountered in some bacteria. Phylogenetic analyses of E. histolytica IscS and IscU showed a close relationship with homologs from Helicobacter pylori and Campylobacter jejuni, to the exclusion of mitochondrial isoforms.

Conclusions: The bacterial-type FeS cluster assembly genes of E. histolytica suggest their lateral acquisition from epsilon proteobacteria. This is a clear example of horizontal gene transfer (HGT) from eubacteria to unicellular eukaryotic organisms, a phenomenon known to contribute significantly to the evolution of eukaryotic genomes.

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Overview of the 5'-flanking region of E. histolytica iscU (A) and iscS (B) encoding genes. The three typical upstream regulatory elements are depicted as by Purdy et al [23]; the putative initiator element, double underlined; the `GAAC'-element, grey box; and the putative TATA element, boxed.
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Figure 1: Overview of the 5'-flanking region of E. histolytica iscU (A) and iscS (B) encoding genes. The three typical upstream regulatory elements are depicted as by Purdy et al [23]; the putative initiator element, double underlined; the `GAAC'-element, grey box; and the putative TATA element, boxed.

Mentions: BLAST searches of preliminary data generated by the E. histolytica genome-sequencing project revealed clones with extensive sequence similarity to the G. intestinalis iscS gene. PCR amplification of E. histolytica genomic DNA using primers based on these putative E. histolytica EhiscS sequences and on a putative EhiscU sequence (accession number: AY040613) generated products of the expected size. DNA sequencing confirmed the identity of the amplified clones. The 5' untranslated regions of EhiscU and EhiscS contain distinct putative promoter elements reported to be typical for E. histolytica [23]. All three conserved regions are present in the first 40 bases upstream the initiation codon of iscU and iscS (Fig. 1), suggesting both genes are functional, although the GAAC-element is less well conserved in the iscU promoter region. The E. histolytica IscU protein is 348 amino acids in length and has a predicted molecular mass of 38.9 kDa and a predicted isoelectric point of 5.71. Its large size indicates it is a long-form IscU, similar to the one described for Azotobacter vinelandii [24], and not a short form as found in other eukaryotes (Fig. 2). For IscS these values are 390 amino acids, 42.8 kDa, and 5.92, respectively. The GC values for the iscU (iscS) genes are 33 % (32 %) for the coding region, 29 % (25 %) for the 5' untranslated region and 29 % (18 %) for the 3' untranslated region (250 bp each). These values are in agreement with GC values reported for other E. histolytica genes based on 75,615 codons analyzed [25]. Codon usage is also similar to E. histolytica codon usage and no introns are present in either of these two genes.


The iron-sulfur cluster assembly genes iscS and iscU of Entamoeba histolytica were acquired by horizontal gene transfer.

van der Giezen M, Cox S, Tovar J - BMC Evol. Biol. (2004)

Overview of the 5'-flanking region of E. histolytica iscU (A) and iscS (B) encoding genes. The three typical upstream regulatory elements are depicted as by Purdy et al [23]; the putative initiator element, double underlined; the `GAAC'-element, grey box; and the putative TATA element, boxed.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC373444&req=5

Figure 1: Overview of the 5'-flanking region of E. histolytica iscU (A) and iscS (B) encoding genes. The three typical upstream regulatory elements are depicted as by Purdy et al [23]; the putative initiator element, double underlined; the `GAAC'-element, grey box; and the putative TATA element, boxed.
Mentions: BLAST searches of preliminary data generated by the E. histolytica genome-sequencing project revealed clones with extensive sequence similarity to the G. intestinalis iscS gene. PCR amplification of E. histolytica genomic DNA using primers based on these putative E. histolytica EhiscS sequences and on a putative EhiscU sequence (accession number: AY040613) generated products of the expected size. DNA sequencing confirmed the identity of the amplified clones. The 5' untranslated regions of EhiscU and EhiscS contain distinct putative promoter elements reported to be typical for E. histolytica [23]. All three conserved regions are present in the first 40 bases upstream the initiation codon of iscU and iscS (Fig. 1), suggesting both genes are functional, although the GAAC-element is less well conserved in the iscU promoter region. The E. histolytica IscU protein is 348 amino acids in length and has a predicted molecular mass of 38.9 kDa and a predicted isoelectric point of 5.71. Its large size indicates it is a long-form IscU, similar to the one described for Azotobacter vinelandii [24], and not a short form as found in other eukaryotes (Fig. 2). For IscS these values are 390 amino acids, 42.8 kDa, and 5.92, respectively. The GC values for the iscU (iscS) genes are 33 % (32 %) for the coding region, 29 % (25 %) for the 5' untranslated region and 29 % (18 %) for the 3' untranslated region (250 bp each). These values are in agreement with GC values reported for other E. histolytica genes based on 75,615 codons analyzed [25]. Codon usage is also similar to E. histolytica codon usage and no introns are present in either of these two genes.

Bottom Line: E. histolytica IscU and IscS were found to contain all features considered essential for their biological activity, including amino acid residues involved in substrate and/or co-factor binding.The bacterial-type FeS cluster assembly genes of E. histolytica suggest their lateral acquisition from epsilon proteobacteria.This is a clear example of horizontal gene transfer (HGT) from eubacteria to unicellular eukaryotic organisms, a phenomenon known to contribute significantly to the evolution of eukaryotic genomes.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Biological Sciences, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK. mark.vandergiezen@rhul.ac.uk

ABSTRACT

Background: Iron-sulfur (FeS) proteins are present in all living organisms and play important roles in electron transport and metalloenzyme catalysis. The maturation of FeS proteins in eukaryotes is an essential function of mitochondria, but little is known about this process in amitochondriate eukaryotes. Here we report on the identification and analysis of two genes encoding critical FeS cluster (Isc) biosynthetic proteins from the amitochondriate human pathogen Entamoeba histolytica.

Results: E. histolytica IscU and IscS were found to contain all features considered essential for their biological activity, including amino acid residues involved in substrate and/or co-factor binding. The IscU protein differs significantly from other eukaryotic homologs and resembles the long type isoforms encountered in some bacteria. Phylogenetic analyses of E. histolytica IscS and IscU showed a close relationship with homologs from Helicobacter pylori and Campylobacter jejuni, to the exclusion of mitochondrial isoforms.

Conclusions: The bacterial-type FeS cluster assembly genes of E. histolytica suggest their lateral acquisition from epsilon proteobacteria. This is a clear example of horizontal gene transfer (HGT) from eubacteria to unicellular eukaryotic organisms, a phenomenon known to contribute significantly to the evolution of eukaryotic genomes.

Show MeSH