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This Week in PNAS: Dec 22, 2009

In this week's PNAS, Wayne State University researchers report on a way to monitor DNA synthesis at the single base-pair level. By looking at single-molecule Förster resonance energy transfer, researchers led by David Rueda were able to see the incorporation of three nucleotides by the Escherichia coli DNA polymerase I. They then noted that the FRET efficiency drops off and then returns the expected level. "The most compelling [explanation] is that the polymerase has transiently moved about one nucleotide increment further along the template than the next preinsertion site," the authors write.

Italian researchers report that in Xenopus, the genes that direct late progenitor cells to become the biopolar neurons of the neural retina are inhibited by microRNAs. Using expression and functional screens, they found four microRNAs that are expressed in the embryonic retina and that bind to the 3'UTRs of those genes. The researchers "propose a model in which the proliferation rate and the age of a retinal progenitor are linked to each other and determine the progenitor fate through the activity of a set of miRNAs."

French scientists studied the role of endo-siRNAs in heterochromatin formation in Drosophila. They used the Tombusvirus P19 and Flock House virus B2 proteins to inhibit endo-siRNA function. P19, they found, sequestered transposable element-derived endo-siRNAs and B2 worked on the long precursors. "Our findings provide evidence that a nuclear pool of TE-derived endo-siRNAs is involved in heterochromatin formation in somatic tissues in Drosophila," the researchers write.

In the early edition of PNAS, researchers led by Samir Mitragotri synthesized biomaterial particles that mimic the key features of red blood cells. They report that these synthetic particles can carry oxygen and move through capillaries and hypothesize that they could be used to carry drugs and in medical imaging.

The Scan

Vaccine Update Recommended

A US Food and Drug Administration panel recommends booster vaccines be updated to target Omicron, CNBC reports.

US to Make More Vaccines for Monkeypox Available

The US is to make nearly 300,000 vaccine doses available in the coming weeks to stem the spread of human monkeypox virus, according to NPR.

Sentence Appealed

The Associated Press reports that Swedish prosecutors are appealing the sentence given to a surgeon once lauded for transplanting synthetic tracheas but then convicted of causing bodily harm.

Genome Biology Papers on COVID-19 Effector Genes, Virtual ChIP-seq, scDART

In Genome Biology this week: proposed COVID-19 effector genes, method to predict transcription factor binding patterns, and more.