Role of E proteins in controlling Notch-mediated T-cell commitment. E protein function, which is inhibited by Id1, controls the transcription of the Gfi1b gene, encoding a known repressor of GATA3 transcription. As a result, elevated levels of GATA3 in T-cell progenitors of Id1 transgenic mice lead to an increase in Deltex1 levels, which interferes with Notch signaling in directing T-cell commitment, as well as Notch autoregulation.