In a paper from Taekjip Ha at the University of Illinois, Urbana-Champaign, and Smita Patel at the University of Medicine and Dentistry of New Jersey that appears in the early online edition of Nature this week, their team found that during DNA replication, RNA primers "are made 'on the fly' during ongoing DNA synthesis and that the leading-strand T7 replisome does not pause during primer synthesis, contrary to previous reports." This accounts for the fact that the two replicating strands are synthesized at the same rate even though two polymerases, leading and lagging strand, are involved.
In Nature this week, which is a third special issue in the magazine's year-long celebration of Charles Darwin, the focus is on preserving biodiversity. Several articles address this theme, with one news feature by Nick Lane looking into the origin of bar codes, the process of indentifying species from the sequence of their mitochondrial DNA.
Led in part by the Salk Institute's Joe Ecker, scientists present the first, genome-wide map at single base pair resolution of cytosine methylation in a mammalian genome, from both human embryonic stem cells and fetal fibroblasts. Their results show key differences in methylation patterns between the two genomes, including that nearly one-quarter of all methylation in embryonic stem cells is non-CG, "suggesting that embryonic stem cells may use different methylation mechanisms to affect gene regulation," they write in the abstract. A News and Views piece offers more.
Scientists led in part by Patrick Cramer at LMU Munich present the crystal structure of the complete RNA polymerase II (Pol II) and transcription factor IIB (B) complex, as well as complementary functional information. The structure's Pol II active center cleft plays a large role in transcription initiation and RNA elongation, the results show. Another News and Views article lends insight.