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Psi-Phi: exploring the outer limits of bacterial pseudogenes.

ABSTRACT: Because bacterial chromosomes are tightly packed with genes and were traditionally viewed as being optimized for size and replication speed, it was not surprising that the early annotations of sequenced bacterial genomes reported few, if any, pseudogenes. But because pseudogenes are generally recognized by comparisons with their functional counterparts, as more genome sequences accumulated, many bacterial pathogens were found to harbor large numbers of truncated, inactivated, and degraded genes. Because the mutational events that inactivate genes occur continuously in all genomes, we investigated whether the rarity of pseudogenes in some bacteria was attributable to properties inherent to the organism or to the failure to recognize pseudogenes. By developing a program suite (called Psi-Phi, for Psi-gene Finder) that applies a comparative method to identify pseudogenes (attributable both to misannotation and to nonrecognition), we analyzed the pseudogene inventories in the sequenced members of the Escherichia coli/Shigella clade. This approach recovered hundreds of previously unrecognized pseudogenes and showed that pseudogenes are a regular feature of bacterial genomes, even in those whose original annotations registered no truncated or otherwise inactivated genes. In Shigella flexneri 2a, large proportions of pseudogenes are generated by nonsense mutations and IS element insertions, events that seldom produce the pseudogenes present in the other genomes examined. Almost all (>95%) pseudogenes are restricted to only one of the genomes and are of relatively recent origin, suggesting that these bacteria possess active mechanisms to eliminate nonfunctional genes.

SUBMITTER: Lerat E

PROVIDER: S-EPMC525686 | biostudies-literature | 2004 Nov

REPOSITORIES: biostudies-literature

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Psi-Phi: exploring the outer limits of bacterial pseudogenes.

Lerat Emmanuelle E Ochman Howard H

Genome research 20041012 11

Because bacterial chromosomes are tightly packed with genes and were traditionally viewed as being optimized for size and replication speed, it was not surprising that the early annotations of sequenced bacterial genomes reported few, if any, pseudogenes. But because pseudogenes are generally recognized by comparisons with their functional counterparts, as more genome sequences accumulated, many bacterial pathogens were found to harbor large numbers of truncated, inactivated, and degraded genes. ...[more]

PMID: 15479949

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Project description:We present an automated method for modeling backbones of protein loops. The method samples a database of phi i + 1 and psi i angles constructed from a nonredundant version of the Protein Data Bank (PDB). The dihedral angles phi i + 1 and psi i completely define the backbone conformation of a dimer when standard bond lengths, bond angles, and a trans planar peptide configuration are used. For the 400 possible dimers resulting from 20 natural amino acids, a list of allowed phi i + 1, psi i pairs for each dimer is created by pooling all such pairs from the loop segments of each protein in the nonredundant version of the PDB. Starting from the N-terminus of the loop sequence, conformations are generated by assigning randomly selected pairs of phi i + 1, psi i for each dimer from the respective pool using standard bond lengths, bond angles, and a trans peptide configuration. We use this database to simulate protein loops of lengths varying from 5 to 11 amino acids in five proteins of known three-dimensional structures. Typically, 10,000-50,000 models are simulated for each protein loop and are evaluated for stereochemical consistency. Depending on the length and sequence of a given loop, 50-80% of the models generated have no stereochemical strain in the backbone atoms. We demonstrate that, when simulated loops are extended to include flanking residues from homologous segments, only very few loops from an ensemble of sterically allowed conformations orient the flanking segments consistent with the protein topology. The presence of near-native backbone conformations for loops from five different proteins suggests the completeness of the dimeric database for use in modeling loops of homologous proteins. Here, we take advantage of this observation to design a method that filters near-native loop conformations from an ensemble of sterically allowed conformations. We demonstrate that our method eliminates the need for a loop-closure algorithm and hence allows for the use of topological constraints of the homologous proteins or disulfide constraints to filter near-native loop conformations.

Dataset Information

Psi-Phi: exploring the outer limits of bacterial pseudogenes.

Publications

Psi-Phi: exploring the outer limits of bacterial pseudogenes.

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