We present an analysis of atmospheric neutrino data from a 33.0 kton yr (535-day) exposure of the Super-Kamiokande detector. The data exhibit a zenith angle dependent deficit of muon neutrinos which is inconsistent with expectations based on calculations of the atmospheric neutrino flux. Experimental biases and uncertainties in the prediction of neutrino fluxes and cross sections are unable to explain our observation. The data are consistent, however, with two-flavor n m $ n t oscillations with sin 2 2u . Atmospheric neutrinos are produced as decay products in hadronic showers resulting from collisions of cosmic rays with nuclei in the upper atmosphere. Production of electron and muon neutrinos is dominated by the processes p 1 ! m 1 1 n m followed by m 1 ! e 1 1 n m 1 n e (and their charge conjugates) giving an expected ratio 1562 0031-9007͞98͞81(8)͞1562(6)$15.00

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Summary Following Cas9 cleavage, DNA repair without a donor template is generally considered stochastic, heterogeneous, and impractical beyond gene disruption. Here, we show that template-free Cas9 editing is predictable and capable of precise repair to a predicted genotype, enabling correction of human disease-associated mutations. We constructed a library of 2,000 Cas9 guide RNAs (gRNAs) paired with DNA target sites and trained inDelphi, a machine learning model that predicts genotypes and frequencies of 1- to 60-bp deletions and 1-bp insertions with high accuracy (r = 0.87) in five human and mouse cell lines. inDelphi predicts that 5–11% of Cas9 gRNAs targeting the human genome are “precise-50”, yielding a single genotype comprising ≥50% of all major editing products. We experimentally confirmed precise-50 insertions and deletions in 195 human disease-relevant alleles, including correction in primary patient-derived fibroblasts of pathogenic alleles to wild-type genotype for Hermansky-Pudlak syndrome and Menkes disease. This study establishes an approach for precise, template-free genome editing.

Broad use of CRISPR-Cas12a (formerly Cpf1) nucleases 1 has been hindered by the requirement for an extended TTTV protospacer adjacent motif (PAM) 2 . To address this limitation, we engineered an enhanced Acidaminococcus sp. Cas12a variant (enAsCas12a) that has a substantially expanded targeting range, enabling targeting of many previously inaccessible PAMs. On average, enAsCas12a exhibits two-fold higher genome editing activity on sites with canonical TTTV PAMs compared to wild-type AsCas12a, and we successfully grafted a subset of mutations from enAsCas12a onto other previously described AsCas12a variants 3 to enhance their activities. enAsCas12a improves the efficiency of multiplex gene editing, endogenous gene activation, and C-to-T base editing, and we engineered a high-fidelity version of enAsCas12a (enAsCas12a-HF1) to reduce off-target effects. Both enAsCas12a and enAsCas12a-HF1 function in HEK293T and primary human T cells when delivered as ribonucleoprotein (RNP) complexes. Collectively, enAsCas12a provides an optimized version of Cas12a that should enable wider application of Cas12a enzymes for gene and epigenetic editing. [AU: Revised abstract OK?]