The function of DTX1 (deltex E3 ubiquitin ligase 1, Ensembl gene identifier ENSG00000135144) is as follows. E3 ubiquitin-protein ligase that mediates ubiquitination and proteasomal degradation of MEKK1, thereby modulating signaling pathways involved in cell fate determination (By similarity). Regulates the Notch signaling pathway, acting predominantly as a positive regulator but functioning as a context-dependent negative regulator in specific developmental or cellular settings. Mediates the antineural activity of Notch signaling, likely by inhibiting transcriptional activation mediated by MATCH1. Negatively regulates Notch signaling by controlling the activity of PIP4K2C, a lipid kinase that promotes recycling of Notch receptors from RAB4A-positive endosomes to the cell surface (PubMed:29440432). Participates in several developmental and immune processes, including neurogenesis, lymphogenesis, and myogenesis. Influences lymphocyte differentiation by promoting B-cell development at the expense of T-cell development, suggesting functional antagonism of NOTCH1 in this context. Also promotes degradation of PRKCQ via the endosome-lysosome pathway, contributing to PKCtheta downregulation during T-cell anergy (PubMed:25000980). In addition, facilitates differentiation of Th17 cells by inducing expression and DNA-binding activity of RORgT (PubMed:32736174). {ECO:0000250|UniProtKB:Q61010, ECO:0000269|PubMed:11564735, ECO:0000269|PubMed:11869684, ECO:0000269|PubMed:25000980, ECO:0000269|PubMed:29440432, ECO:0000269|PubMed:32736174, ECO:0000269|PubMed:9590294}.