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This Week in PNAS: Jun 14, 2011

In the PNAS Early Edition this week, a trio of investigators at the University of California, Berkeley, discuss what they call "the fundamental relationship between operon organization and gene expression." Using synthetic operons in E. coli, the team shows that "the expression of a given gene increases with the length of the operon and as its position moves farther from the end of the operon." The Berkeley team says that increasing the transcription distance — that is, "the distance from the start of a gene to the end of the operon" — allows more time for translation to occur, and therefore results in increased expression. Overall, the team says that a "fundamental relationship exists between gene expression and the number, length, and order of the genes in an operon," and that "this relationship has important implications for understanding the functional basis of genome organization and practical applications for synthetic biology."

A public-private team led by researchers at Seoul National University reports on its identification of microRNA signatures in undifferentiated blastoderm and primordial germ cells of chicken. The team found seven miRNAs that are highly expressed in the former and 10 that are highly expressed in the latter. The team then examined "miR-302a and miR-456 for blastoderm and miR-181a[-star] for PGCs" further, finding that "both miR-302a and miR-456 bound directly to the sex-determining region Y box 11 transcript and could act as posttranscriptional co-regulators to maintain the undifferentiated state of the chicken blastoderm through the suppression of somatic gene expression and differentiation." The team concludes that, "in chickens, miRNAs intrinsically regulate the differentiation fate of blastoderms and PGCs," and, in addition, "that the specific timing of germ cell meiosis is controlled through miRNA expression," it writes in PNAS.

Researchers in Switzerland this week present PANTHERE — pan-genomic translocation for heterologous enhancer reshuffling. In applying the approach to analyze Hox gene clusters, the team found that whole-genome duplications "favored the appearance of distinct global regulations." PANTHERE, the authors write, allowed them to "bring the entire megabase-scale HoxD regulatory landscape in front of the HoxC gene cluster via a targeted translocation in vivo.," and thus to find that "Hoxc genes could both interpret this foreign regulation and functionally substitute for their Hoxd counterparts."

The University of Oxford's Xindan Wang et al. this week report their generation of E. coli cells "with two WT [wild-type] origins separated by 1 Mb in their 4.64-Mb chromosome," with which they observed "productive bi-directional replication [that] initiated synchronously at both spatially separate origins." The new DNA from both "segregated sequentially as replication progressed, with two temporally and spatially separate replication termination events," Wang et al. add.

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