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This Week in PNAS: Oct 29, 2013

In the early, online edition of the Proceedings of the National Academy of Sciences, a team from Italy and the US describes patterns found in the genomes of symbiotic and free-living Polynucleobacter necessarius — a bacterial species expected to offer clues about processes that can contribute to genome reduction. By sequencing the genome of symbiotic P. necessarius representatives found in the cytoplasm of a protist called Euplotes aediculatus and comparing the sequence to P. necessarius genomes sequenced in the past, the researchers garnered genetic insights into the bug's metabolic capabilities, both in its free-living state and in Euplotes. In addition, they examined sequences that have been jettisoned from the already compact P. necessarius genome during the shift to a symbiotic lifestyle.

Princeton University and Santa Clara University researchers report on a study of heat stress survival genes in the yeast model organism Saccharomyces cerevisiae. The team tracked heat response starting from a set of 4,800 barcoded, budding yeast strains, each characterized by a different non-essential gene deletion. With the help of barcode sequencing, they were subsequently able to identify genetic contributors during heat stress, including members of metabolic, chromatin, and other pathways. That gene set was largely independent of the genes up regulated in heat-exposed yeast, the study authors found. "We suggest that survival after heat shock depends on a small number of genes that function in assessing the metabolic health of the cell and/or regulate its growth in a changing environment," they write.

The University of California, Davis' Carlos Ueira-Vieira and colleagues used RNA sequencing to delve into the source of the southern house mosquito's acute sense of smell. By comparing the transcript sequences present in mosquitoes' non-olfactory tissues with those found in antennae — which is responsible for most of the insect's olfactory wherewithal — the researchers narrowed in on differentially expressed genes that seem to boost the southern mosquito's sniffing skills. After verifying the up-regulation of olfaction-related sequences by quantitative, real-time PCR, the group expressed one of the odorant receptor genes in mosquito oocytes before using a chemical screen to home in on compounds that appear to repel mosquitoes.