This week in the PNAS Early Edition, the University of Oxford's Pietro Roversi et al. report their characterization of the "structural basis for complement factor I control and its disease-associated sequence polymorphisms." In working out the crystal structure of the complement regulatory enzyme human factor I, or fI, and mapping functional data from fI mutants onto it, the team observed structural properties that serve to explain "the molecular basis of disease-associated polymorphisms in fI and its cofactors," the authors write.
Elsewhere, researchers at the University of Pennsylvania show that transient inhibition of miR-21 in spermatogonial stem cell-enriched germ cell cultures leads to an increase in "the number of germ cells undergoing apoptosis and significantly reduced the number of donor-derived colonies of spermatogenesis formed from transplanted treated cells in recipient mouse testes, indicating that miR-21 is important in maintaining the SSC [spermatogonial stem cell] population."
The National Institutes of Health's Hope Cole, Bruce Howard, and David Clark show in PNAS this week that "the centromeric nucleosome of budding yeast is perfectly positioned and covers the entire centromere." This, the trio says, has functional consequences. In the centromeric nucleosomes of budding yeast, the authors write, "the entire centromere is included," as are stretches of DNA upstream and downstream of the Cbf1 and CBF3 sites, respectively. "That the binding sites for Cbf1 and CBF3 are included within the centromeric nucleosome has important implications for models of the centromeric nucleosome and for kinetochore function," Cole and her colleagues write.
In another nucleosome-centric paper published online in advance this week, Ohio State University's Michael Poiriera et al. show that histone post-translational modifications "within distinct structured regions of the nucleosome directly regulate the inherent dynamic properties of the nucleosome." In its FRET and restriction enzyme-based analyses, the team found that only those post-translational modifications "throughout the DNA entry-exit region increase unwrapping and enhance transcription factor binding to nucleosomal DNA," thus providing support for the idea that histone post-translational modifications "may independently influence nucleosome dynamics and associated chromatin functions," the authors write.