We have isolated a new gene, psu1(+), from the fission yeast Schizosaccharomyces pombe. The predicted amino acid sequences shows that this protein has striking homology to the SUN family of the budding yeast, hence designated Psu1 (S. pombe homologue of the SUN family). Disruption of the psu1(+) gene revealed that it is essential for growth, and the null phenotype showed the swelling of cells followed by eventual lysis. We introduced psu1(+) gene in the disruptant strain and repressed it giving resistance to 1, 3-beta-glucanase digestion. Our results suggest that Psu1 plays an essential role in cell wall synthesis in S. pombe.