I-POU: a POU-domain protein that inhibits neuron-specific gene activation.

A novel, structurally distinct POU-domain protein has been identified that inhibits activation by another positive POU-domain regulator of neuron-specific transcription units. Two Drosophila POU-domain proteins, I-POU and Cf1-a, are coexpressed in overlapping subsets of neurons during development. Because I-POU lacks two basic residues in the N terminus of its homeodomain, it cannot bind DNA, but it does form a stable heterodimeric complex with Cf1-a, preventing Cf1-a from binding to DNA recognition elements and from transactivating the dopa-decarboxylase gene. The inhibition by I-POU provides a potential strategy by which the activation of genes in development is controlled by a homeodomain-containing protein that does not bind DNA.