Nuclear migration is essential for normal development in both higher and lower eukaryotes. Four genes involved in nuclear migration in Aspergillus nidulans (nudA, nudG, nudC and nudF) have been cloned. NUDA and NUDG have been shown to be the dynein heavy chain and a dynein light chain, respectively. The nudC gene encodes a 23 Kd protein whose homologues have been found in Drosophila, rat, and human, but its biological function is unknown. The nudF gene was cloned as an extracopy suppressor of the nudC3 mutation. Its expression is decreased by the nudC3 mutation. We further investigated the biological functions of nudC. We show, surprisingly, deletion of nudC causes a deleterious effect on cell morphology, development and viability, which is different from the deletion of either nudA or nudF. This strongly suggests that the nudC gene is an essential gene and may be involved in biological events other than nuclear migration. Moreover NUDC protein was not detected at a lower temperature (18), suggesting that expression of the nudC gene is highly regulated. We also observed that unlike the nudC3 mutation, deletion of nudC does not affect the NUDF level.