A new member in the Argonaute crew: the mt-miRNAs

SummaryMutations within the mitochondrial genome have been linked to many diverse phenotypes. Moreover, the effects of these mutations have been shown to differ across sexes and environments. The mechanisms that explain the manifold array of mitochondrial genotypic effects on organismal function, and their context-dependency, have however remained a mystery. Here, we present evidence that mitochondria are involved in nuclear gene regulation via RNA interference; transcribing mitochondrial (mt-)miRNAs that may repress the transcription of nuclear genes that previously had no known involvement in mitochondrial function. Our findings uncover a new mechanism by which mitochondria may shape the expression of animal life-histories and health components; implying that the influence of the mitochondria in regulating organismal function extends well beyond the process of energy production.

A crystallographic study of human NONO (p54nrb): overcoming pathological problems with purification, data collection and noncrystallographic symmetry

Non-POU domain-containing octamer-binding protein (NONO, a.k.a. p54nrb) is a central player in nuclear gene regulation with rapidly emerging medical significance. NONO is a member of the highly conservedDrosophilabehaviour/human splicing (DBHS) protein family, a dynamic family of obligatory dimeric nuclear regulatory mediators. However, work with the NONO homodimer has been limited by rapid irreversible sample aggregation. Here, it is reported that L-proline stabilizes purified NONO homodimers, enabling good-quality solution small-angle X-ray structure determination and crystallization. NONO crystallized in the apparent space groupP21with a unique axis (b) of 408.9 Å and with evidence of twinning, as indicated by the cumulative intensity distributionLstatistic, suggesting the possibility of space groupP1. Structure solution by molecular replacement shows a superhelical arrangement of six NONO homodimers (or 12 inP1) oriented parallel to the long axis, resulting in extensive noncrystallographic symmetry. Further analysis revealed that the crystal was not twinned, but the collected data suffered from highly overlapping reflections that obscured theL-test. Optimized data collection on a new crystal using higher energy X-rays, a smaller beam width and an increased sample-to-detector distance produced non-overlapping reflections to 2.6 Å resolution. The steps taken to analyse and overcome this series of practical difficulties and to produce a biologically informative structure are discussed.