In PLoS Genetics this week, researchers in the UK and New York have identified endogenous viral elements derived from 10 non-retroviral families using systematic in silico screening of animal genomes. "Integration into the nuclear genome of germ line cells can lead to vertical inheritance of retroviral genes as host alleles," the researchers write. In performing phylogenetic and genomic analysis of these viral elements across multiple host species, the team found novel information about the origin and evolution of various virus groups. "For one element in the primate lineage, we provide statistically robust evidence for exaptation," the researchers write. "Our findings establish that genetic material derived from all known viral genome types and replication strategies can enter the animal germ line … indicating a more significant evolutionary role for gene flow from virus to animal genomes than has previously been recognized."
In PLoS One this week, researchers in Seattle led by Mary Lidstrom used a systems biology approach to uncover cellular strategies used by Methylobacterium extorquens during the switch from multi- to single-carbon growth. The study focused on the mechanisms of metabolic adaptation that occur during the bacterium's transition from succinate growth to methanol growth. "This approach has resulted in new insights into the metabolic strategies carried out to effect this shift between two dramatically different modes of growth and identified a number of potential flux control and regulatory check points as a further step toward understanding metabolic adaptation and the cellular strategies employed to maintain metabolic setpoints," the researchers write.
In PLoS Biology this week, researchers in Canada and Israel suggest that subtle alterations in proliferating cell nuclear antigen-partner interactions severely impair DNA replication and repair. The researchers generated and characterized PCNA mutants with increased attraction to key partners in the PCNA-partner network and found that increases in these partner interactions can lead to severe in vivo phenotypic defects. "The subtle and tunable nature of these affinity perturbations produced different phenotypic effects than realized with traditional 'on-off' analysis using gene knockouts," the team writes. "Our findings indicate that biological systems can be robust to one set of perturbations yet fragile to others."
Also in PLoS Biology this week, researchers in Maryland elucidate the role of the sister chromatid in the repair of DNA double-strand breaks during budding yeast meiosis. In examining events initiated by double-strand breaks in regions that lack corresponding sequences on the homolog, the researchers showed that these breaks are efficiently repaired by inter-sister recombination. This occurs at the same time as inter-homolog recombination but with reduced yields of joint molecules, the researchers suggest. They add, "These findings indicate that inter-sister recombination occurs frequently during budding yeast meiosis, with the possibility that up to one-third of all recombination events occur between sister chromatids."