The moc3 gene was screened out as an inducer of sexual differentiation in fission yeast Schizosaccharomyces pombe. We isolated a novel gene, named ers2, encoding mitochondrial glutamyl tRNA synthetase (mGluRS) as a Moc3 interacting element by the yeast two-hybrid system. Cytoplasmic glutamyl tRNA synthetase (cGluRS) also interacted with Moc3 in a yeast two-hybrid system. Disruption of ers1 (cGluRS) and of ers2 (mGluRS) indicated that these genes are both essential for the cell growth of S. pombe. We found that ers2 severely affected cell growth and decreased viability, but induced sexual differentiation of S. pombe when it was over-expressed. Over-expression of ers1 also stimulated sexual differentiation in S. pombe. These observations led us to test the effects of various amino acids on sexual differentiation. We found that glutamic acid, as well as other specific amino acids, such as tryptophan, methionine, and threonine, efficiently induced sexual differentiation in S. pombe. Our findings suggest a new regulatory mechanism where GluRSs and glutamic acid are involved in sexual differentiation in S. pombe.