Information Génomique et Structurale, CNRS-UPR2589, Institut de Microbiologie de la Méditerranée, Parc Scientifique de Luminy, Aix-Marseille Université, Marseille Cedex 9, France.
ISME J. 2011 Jul;5(7):1143-51. doi: 10.1038/ismej.2010.210. Epub 2011 Jan 20.
MutS proteins are ubiquitous in cellular organisms and have important roles in DNA mismatch repair or recombination. In the virus world, the amoeba-infecting Mimivirus, as well as the recently sequenced Cafeteria roenbergensis virus are known to encode a MutS related to the homologs found in octocorals and ɛ-proteobacteria. To explore the presence of MutS proteins in other viral genomes, we performed a genomic survey of four giant viruses ('giruses') (Pyramimonas orientalis virus (PoV), Phaeocystis pouchetii virus (PpV), Chrysochromulina ericina virus (CeV) and Heterocapsa circularisquama DNA virus (HcDNAV)) that infect unicellular marine algae. Our analysis revealed the presence of a close homolog of Mimivirus MutS in all the analyzed giruses. These viral homologs possess a specific domain structure, including a C-terminal HNH-endonuclease domain, defining the new MutS7 subfamily. We confirmed the presence of conserved mismatch recognition residues in all members of the MutS7 subfamily, suggesting their role in DNA mismatch repair rather than DNA recombination. PoV and PpV were found to contain an additional type of MutS, which we propose to call MutS8. The MutS8 proteins in PoV and PpV were found to be closely related to homologs from 'Candidatus Amoebophilus asiaticus', an obligate intracellular amoeba-symbiont belonging to the Bacteroidetes. Furthermore, our analysis revealed that MutS7 and MutS8 are abundant in marine microbial metagenomes and that a vast majority of these environmental sequences are likely of girus origin. Giruses thus seem to represent a major source of the underexplored diversity of the MutS family in the microbial world.
MutS 蛋白在细胞生物中普遍存在，在 DNA 错配修复或重组中具有重要作用。在病毒世界中，已发现感染变形虫的 Mimivirus 以及最近测序的 Cafeteria roenbergensis 病毒编码与八放珊瑚和 ε-变形菌同源的 MutS 相关蛋白。为了探索 MutS 蛋白在其他病毒基因组中的存在，我们对感染单细胞海洋藻类的四种巨型病毒（“giruses”）（Pyramimonas orientalis virus (PoV)、Phaeocystis pouchetii virus (PpV)、Chrysochromulina ericina virus (CeV) 和 Heterocapsa circularisquama DNA virus (HcDNAV)）进行了基因组调查。我们的分析表明，在所有分析的 giruses 中都存在 Mimivirus MutS 的紧密同源物。这些病毒同源物具有特定的结构域，包括 C 末端 HNH 内切酶结构域，定义了新的 MutS7 亚家族。我们证实了所有 MutS7 亚家族成员中保守的错配识别残基的存在，这表明它们在 DNA 错配修复而不是 DNA 重组中的作用。PoV 和 PpV 被发现含有另一种类型的 MutS，我们称之为 MutS8。PoV 和 PpV 中的 MutS8 蛋白与“Candidatus Amoebophilus asiaticus”的同源物密切相关，后者是一种专性细胞内变形虫共生菌，属于 Bacteroidetes。此外，我们的分析表明，MutS7 和 MutS8 在海洋微生物宏基因组中丰富存在，并且这些环境序列的绝大多数可能来自 giruses。因此，giruses 似乎是微生物世界中 MutS 家族未被充分探索多样性的主要来源。
