Mixed synthetic oligonucleotides encoding a sequence conserved among tyrosine-specific protein kinases were used to probe the genome of the fission yeast Schizosaccharomyces pombe. A single gene (kin1+) was isolated that encodes a putative protein kinase closely related to the KIN1- and KIN2-encoded serine/threonine-specific protein kinases of Saccharomyces cerevisiae. kin1+ is transcribed into a 3.5-kilobase mRNA that contains an uninterrupted open reading frame encoding a polypeptide of 98 kDa. In contrast to results obtained with kin mutants of S. cerevisiae, disruption of the Sc. pombe kin1+ gene resulted in recessive morphological and growth defects. kin1-disrupted cells grew slowly on enriched medium and grew as spheres, in contrast to wild-type Sc. pombe cells, which grow as rods. Relative to kin1+ cells, kin1-disrupted cells were differentially sensitive to lysis by treatment with alpha- and beta-glucanases, suggesting an alteration in either the composition or the organization of their cell walls.