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Highlights d The ciliate methyltransferase MTA1c mediates DNA N6adenine methylation (6mA) d 6mA directly disfavors nucleosome occupancy in vitro d Synthesis of complete, epigenetically defined Oxytricha chromosomes

Network (OPTN) revised the US adult heart allocation policy, intending to address several deficiencies identified in the old system, including an overabundance of candidates with highly diverse urgency within the most urgent status (1A), a large number of exception requests, the increasing use of mechanical circulatory support devices (MCSD) and associated complications unaccounted for in policy, and a geographic sharing scheme that was inconsistent with the Final Rule. 1-4 Prior to the policy modifications, the US heart allocation policy stratified heart transplant candidates into 3 statuses based on the severity of illness, the need for mechanical or pharmacological circulatory support, and complications of the underlying disease or treatment. Adult heart allocation has historically been driven by predicted waiting list mortality and relies on the centers, physicians, and hospitals to transplant candidates that they feel will

BackgroundWhole-genome shotgun sequencing, which stitches together millions of short sequencing reads into a single genome, ushered in the era of modern genomics and led to a rapid expansion of the number of genome sequences available. Nevertheless, assembly of short reads remains difficult, resulting in fragmented genome sequences. Ultimately, only a sequencing technology capable of capturing complete chromosomes in a single run could resolve all ambiguities. Even “third generation” sequencing technologies produce reads far shorter than most eukaryotic chromosomes. However, the ciliate Oxytricha trifallax has a somatic genome with thousands of chromosomes averaging only 3.2 kbp, making it an ideal candidate for exploring the benefits of sequencing whole chromosomes without assembly.ResultsWe used single-molecule real-time sequencing to capture thousands of complete chromosomes in single reads and to update the published Oxytricha trifallax JRB310 genome assembly. In this version, over 50% of the completed chromosomes with two telomeres derive from single reads. The improved assembly includes over 12,000 new chromosome isoforms, and demonstrates that somatic chromosomes derive from variable rearrangements between somatic segments encoded up to 191,000 base pairs away. However, while long reads reduce the need for assembly, a hybrid approach that supplements long-read sequencing with short reads for error correction produced the most complete and accurate assembly, overall.ConclusionsThis assembly provides the first example of complete eukaryotic chromosomes captured by single sequencing reads and demonstrates that traditional approaches to genome assembly can mask considerable structural variation.