A novel 5'-hydroxyl dinucleotide hydrolase activity for the DXO/Rai1 family of enzymes.

Modifications at the 5'-end of RNAs play a pivotal role in determining their fate. In eukaryotes, the DXO/Rai1 family of enzymes removes numerous 5'-end RNA modifications, thereby regulating RNA turnover. Mouse DXO catalyzes the elimination of incomplete 5'-end caps (including pyrophosphate) and the non-canonical NAD+ cap on mRNAs, and possesses distributive 5'-3' exoribonuclease activity toward 5'-monophosphate (5'-PO4) RNA. Here, we demonstrate that DXO also catalyzes the hydrolysis of RNAs bearing a 5'-hydroxyl group (5'-OH RNA). The crystal structure of DXO in complex with a 5'-OH RNA substrate mimic at 2.0 Å resolution provides elegant insight into the molecular mechanism of this activity. More importantly, the structure predicts that DXO first removes a dinucleotide from 5'-OH RNA. Our nuclease assays confirm this prediction and demonstrate that this 5'-hydroxyl dinucleotide hydrolase (HDH) activity for DXO is higher than the subsequent 5'-3' exoribonuclease activity for selected substrates. Fission yeast Rai1 also has HDH activity although it does not have 5'-3' exonuclease activity, and the Rat1-Rai1 complex can completely degrade 5'-OH RNA. An Arabidopsis DXO1 variant is active toward 5'-OH RNA but prefers 5'-PO4 RNA. Collectively, these studies demonstrate the diverse activities of DXO/Rai1 and expands the collection of RNA substrates that can undergo 5'-3' mediated decay.

Arabidopsis DXO1 links RNA turnover and chloroplast function independently of its enzymatic activity.

The DXO family of proteins participates in eukaryotic mRNA 5'-end quality control, removal of non-canonical NAD+ cap and maturation of fungal rRNA precursors. In this work, we characterize the Arabidopsis thaliana DXO homolog, DXO1. We demonstrate that the plant-specific modification within the active site negatively affects 5'-end capping surveillance properties of DXO1, but has only a minor impact on its strong deNADding activity. Unexpectedly, catalytic activity does not contribute to striking morphological and molecular aberrations observed upon DXO1 knockout in plants, which include growth and pigmentation deficiency, global transcriptomic changes and accumulation of RNA quality control siRNAs. Conversely, these phenotypes depend on the plant-specific N-terminal extension of DXO1. Pale-green coloration of DXO1-deficient plants and our RNA-seq data reveal that DXO1 affects chloroplast-localized processes. We propose that DXO1 mediates the connection between RNA turnover and retrograde chloroplast-to-nucleus signaling independently of its deNADding properties.

Defective XRN3-mediated transcription termination in Arabidopsis affects the expression of protein-coding genes.

Arabidopsis thaliana contains two nuclear XRN2/3 5'-3' exonucleases that are homologs of yeast and human Rat1/Xrn2 proteins involved in the processing and degradation of several classes of nuclear RNAs and in transcription termination of RNA polymerase II. Using strand-specific short read sequencing we show that knockdown of XRN3 leads to an altered expression of hundreds of genes and the accumulation of uncapped and polyadenylated read-through transcripts generated by inefficiently terminated Pol II. Our data support the notion that XRN3-mediated changes in the expression of a subset of genes are caused by upstream read-through transcription and these effects are enhanced by RNA-mRNA chimeras generated in xrn3 plants. In turn, read-through transcripts that are antisense to downstream genes may trigger production of siRNA. Our results highlight the importance of XRN3 exoribonuclease in Pol II transcription termination in plants and show that disturbance in this process may significantly alter gene expression.

A survey of positive airway pressure therapy preparedness and outcomes following Hurricane Irma in patients with obstructive sleep apnea.

STUDY OBJECTIVES: Clinical benefit from positive pressure therapy is dependent on treatment adherence. Extreme weather events, such as floods, hurricanes, and tornadoes, can contribute to nonadherence by electricity loss and mandatory evacuation. We aimed to evaluate the concerns and behaviors of regular positive airway pressure users surrounding the extreme weather event Hurricane Irma. METHODS: A questionnaire on positive pressure concerns surrounding Hurricane Irma was completed by 117 patients with pre-hurricane objectively confirmed treatment adherence as defined by Medicare. Responses were tabulated to identify concerns and behavior in preparation for and after Hurricane Irma. Cloud-based monitoring, available on 50 (43%) cases, was used to determine the effect of self-reported electricity loss on treatment adherence before and after the storm. Quantitative use data pre- and post-Hurricane Irma was compared by t test with P < .05 considered statistically significant. RESULTS: Post-hurricane 78 (67%) patients were unable to use treatment with mean duration of 4.3 days. Of these, snoring, choking, and sleepiness were reported in 64%, 19%, and 42%, respectively. Loss of electricity was identified as the cause of missed treatment in 71 patients. In those with cloud monitoring, mean 14-day pre- and post-hurricane use differed by 8 minutes (P =.056). Cloud-monitored cases with loss of electricity had a decline in mean use of 33 minutes for the first 7 days post-hurricane. There was a trend towards increased use post-hurricane in those that retained electricity. Many patients expressed dissatisfaction with the availability of preparedness guidelines. CONCLUSIONS: Although common, loss of electricity was not the sole disruptor of positive pressure use after extreme weather events. Regular users of positive airway pressure experience both disruption in patterns of use and concerns regarding preparedness for extreme weather events.

Perspective: Sleep at the USA Science and Engineering Festival-A New Outreach for the American Academy of Sleep Medicine.

ABSTRACT: This April, the American Academy of Sleep Medicine (AASM) took part as exhibitors at the USA Science and Engineering Festival in Washington, DC. This was AASM's first time attending the festival which is the largest conference of its kind promoting and celebrating science and technology in the United States hosting 370,000 attendees including schoolchildren, educators, and the general public. The AASM's exhibit featured interactive games as well as materials aimed at the promotion of healthy sleep habits in all age groups. A few individuals presented with more specific questions and were provided education and directed to online resources approved by the Academy. It was apparent that many people were unaware of the field of sleep medicine and responded favorably to our presence. We hope our account of the experience helps inform thought on further direction the AASM takes in the realm of public outreach and education.