Several microbial genomes lack textbook-defined essential genes. If an essential gene is absent from a genome, then an evolutionarily independent gene of unknown function complements its function. Here, we identified frequent nonhomologous replacement of an essential component of DNA replication initiation, a replicative helicase loader gene, in . Our analysis of genomes revealed two genes with unknown function, named and , that were substantially enriched in genomes without the known helicase-loader genes. These genes showed no sequence similarities to genes with known function but encoded proteins structurally similar with a viral helicase loader. Analyses of genomic syntenies and coevolution with helicase genes suggested that encodes a helicase loader. The in vitro assay showed that VdhL1 and VdhL2 promote the helicase activity of DnaB. Furthermore, molecular phylogenetics suggested that / were derived from phages and replaced an intrinsic helicase loader gene of over 20 times. This high replacement frequency implies the host's advantage in acquiring a viral helicase loader gene.
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| http://dx.doi.org/10.1073/pnas.2317954121 | DOI Listing |
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