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This Week in PNAS: Aug 25, 2015

In the early, online edition of the Proceedings of the National Academy of Sciences, researchers from France present evidence for past interactions between the unicellular algal species Bigelowiella natans and giant viruses known as nucleocytoplasmic large DNA viruses (NCLDV). By sifting through genome sequences for more than 1,100 sequenced eukaryotes, the team saw some 300 genes in the B. natans genome that appeared to have originated in virophages, suggesting the alga had encountered giant virus that the double-stranded DNA virophages prey on. Through transcriptome sequencing, the study's authors found that these virophages are expressed in multiple Bigelowiella isolates, while sequences that appear to have originated in giant viruses seem to have been inserted elsewhere in the genome.

Researchers from Italy used a genome-wide small interfering RNA screen to find human genes mediating the transduction of adeno-associated viruses (AAV) — viral vectors being explored for in in vivo gene transfer experiments. Using library of small RNAs that target more than 18,100 human genomes, the team screened a human cell line to find knockdowns that altered the activity of an AAV reporter construct. The experiment uncovered almost 1,500 gene that diminished or enhanced the transduction efficiency of the viral vector by between four- and 50-fold, the study's authors say, noting that the results "can be exploited for the development of more efficient AAV-based gene delivery procedures."

Finally, a Memorial Sloan Kettering Cancer Center team presents new insights into the interactions made by the acetyltransferase enzymes Esco1 and Esco2, which modify a cohesin subunit in ways that make it possible for sister chromatids to stick together during the appropriate stage of the cell cycle. Based on chromatin immunoprecipitation and sequencing experiments, the researchers found that Esco1 seems to get recruited by cohesin at more than 11,000 sites genome-wide, while Esco2 tends to show more limited interactions, appearing controlled by transcription factors that target neuron-specific genes. "Together," they write, "our results reveal how vertebrate [cohesin acetyltransferases] have evolved to control multiple aspects of chromosome metabolism in somatic cells."