Catalyzes the reversible stereospecific interconversion of fumarate to L-malate (PubMed:3040736, PubMed:11585823, PubMed:1587456, PubMed:20231875). In mitochondrion, catalyzes the hydration of fumarate to L-malate in the tricarboxylic acid (TCA) cycle to facilitate a transition step in the production of energy in the form of NADH (PubMed:1587456, PubMed:20231875). In cytoplasm and nucleus, involved in DNA repair in response to DNA damage: following DNA double-strand breaks (DSBs), translocates from the cytosol to the nucleus and promotes DNA repair by catalyzing the dehydration of L-malate to fumarate (PubMed:20231875). (S)-malate = fumarate + H2O Carbohydrate metabolism; tricarboxylic acid cycle; (S)-malate from fumarate: step 1/1. Homotetramer. Mitochondrial, cytoplasmic and nuclear forms are derived from a single translation product and not by alternative initiation of the transcript (PubMed:11585823). The mitochondrial transit peptide is cleaved by the mitochondrial processing peptidase, promoting mitochondrial targeting of around 70% of the proteins (PubMed:11585823). The remaining 30% of the processed proteins localize in the cytosol: they probably undergo rapid folding into an import-incompetent state, leading to retrograde movement of the processed proteins back to the cytosol through the translocation pore (PubMed:11585823). Translocates from the cytosol to the nucleus in response to DNA damage (PubMed:20231875). Cells accumulate extracellular fumarate. Present with 6920 molecules/cell in log phase SD medium. There are 2 substrate-binding sites: the catalytic A site, and the non-catalytic B site that may play a role in the transfer of substrate or product between the active site and the solvent. Alternatively, the B site may bind allosteric effectors. Belongs to the class-II fumarase/aspartase family. Fumarase subfamily.