The application of forward genetic screens to cultured human cells represents a powerful method to study gene function. The repurposing of the bacterial CRISPR/Cas9 system provides an effective method to disrupt gene function in mammalian cells, and has been applied to genome-wide screens. Here, we compare the efficacy of genome-wide CRISPR/Cas9-mediated forward genetic screens versus gene-trap mutagenesis screens in haploid human cells, which represent the existing 'gold standard' method. This head-to-head comparison aimed to identify genes required for the endoplasmic reticulum-associated degradation (ERAD) of MHC class I molecules. The two approaches show high concordance (>70%), successfully identifying the majority of the known components of the canonical glycoprotein ERAD pathway. Both screens also identify a role for the uncharacterized gene TXNDC11, which we show encodes an EDEM2/3-associated disulphide reductase. Genome-wide CRISPR/Cas9-mediated screens together with haploid genetic screens provide a powerful addition to the forward genetic toolbox.This work was supported by the Wellcome Trust, through a Principal Research Fellowship to P.J.L. and PhD studentships to S.A.M. and I.A.T., the NIHR Cambridge BRC and the Lundbeck Foundation (L.C.C. and L.E.). The CIMR is in receipt of a Wellcome Trust strategic award.This is the final version of the article. It first appeared from Nature Publishing Group via http://dx.doi.org/10.1038/ncomms11786
