Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Munc18a Scaffolds SNARE Assembly to Promote Membrane Fusion

Munc18a is an SM protein required for SNARE-mediated fusion. The molecular details of how Munc18a acts to enhance neurosecretion have remained elusive. Here, we use in vitro fusion assays to characterize how specific interactions between Munc18a and the neuronal SNAREs enhance the rate and extent of fusion. We show that Munc18a interacts directly and functionally with the preassembled t-SNARE complex. Analysis of Munc18a point mutations indicates that Munc18a interacts with helix C of the Syntaxin1a NRD in the t-SNARE complex. Replacement of the t-SNARE SNAP25b with yeast Sec9c had little effect, suggesting that Munc18a has minimal contact with SNAP25b within the t-SNARE complex. A chimeric Syntaxin built of the Syntaxin1a NRD and the H3 domain of yeast Sso1p and paired with Sec9c eliminated stimulation of fusion, suggesting that Munc18a/Syntaxin1a H3 domain contacts are important. Additionally, a Syntaxin1A mutant lacking a flexible linker region that allows NRD movement abolished stimulation of fusion. These experiments suggest that Munc18a binds to the Syntaxin1a NRD and H3 domain within the assembled t-SNARE complex, positioning them for productive VAMP2 binding. In this capacity, Munc18a serves as a platform for trans-SNARE complex assembly that facilitates efficient SNARE-mediated membrane fusion