Drosophila Enhancer of Rudimentary Homolog, ERH, Is a Binding Partner of RPS3, RPL19, and DDIT4, Suggesting a Mechanism for the Nuclear Localization of ERH

The protein enhancer of rudimentary homolog, ERH, is a small, highly conserved protein that has been found in animals, plants, and protists. Genetic and biochemical interactions have implicated ERH in the regulation of pyrimidine biosynthesis, DNA replication, transcription, mRNA splicing, cellular proliferation, tumorigenesis, and the Notch signaling pathway. In vertebrates and insects, ERH is nuclearly localized; however, an examination of the ERH amino-acid sequence does not reveal any nuclear localization signals. In this paper we show that the first 24 amino acids contain sequences necessary and sufficient for nuclear localization. Through yeast two-hybrid screens, three new binding partners of ERH, RPS3, RPL19, and DDIT4, were identified. RPS3 was isolated from both human and Drosophila screens. These interactions suggest functions of ERH in cell growth, cancer, and DNA repair. The ERH sequences necessary for the interactions between ERH and RPS3 and RPL19 are mapped onto the same 24-amino-acid region in ERH which are necessary for nuclear localization, suggesting that ERH is localizing to the nucleus through binding to one of its DNA-binding partners, such as RPS3 or RPL19.