The gene SCM4 encodes a protein which suppresses a temperature-sensitive allele of the cell division cycle gene CDC4 in Saccharomyces cerevisiae. SCM4 was cloned on a 1.8 kb BamHI fragment of yeast genomic DNA in the high copy-number vector pJDB207, which results in a 50- to 100-fold increase in the level of the 700 nucleotide SCM4 transcript in vivo. The SCM4 gene encodes a 20.2 kDa protein of 187 amino-acids with a clear tripartite domain structure in which a region rich in charged residues separates two domains of largely uncharged amino acids. Although the apparent allele specificity of cdc4 suppression suggests that the CDC4 and SCM4 proteins interact, disruption of SCM4 demonstrates that the gene product is not essential for mitosis or meiosis; however, it may be a member of a family of related, functionally redundant proteins.