A possible interaction between aconitase and a mitochondrial ribosomal protein was suggested in a genome-wide interactome study. In fission yeast Schizosaccharomyces pombe, the aco2(+) gene encodes a fusion protein between aconitase and a putative mitochondrial ribosomal protein bL21 (Mrpl49). Two types of aco2(+) transcripts are generated via alternative poly (A) site selection, producing both a single aconitase domain protein and the fusion form. The bL21-fused Aco2 protein resides in mitochondria as well as in the cytosol and the nucleus. The viability defect of aco2 mutation is complemented not by the aconitase domain but by the bL21 domain, which enables mitochondrial translation. 