Amino acid compositions of all genes in Saccharomyces cerevisiae were determined using a computer analysis of the complete genome. The amino acid composition of an assembly of several genes or a single gene consisted of 3000-7000 amino acid residues forming a certain pattern of amino acid composition. This rule was independent not only of the gene size, but also of the gene position. Thus, the small units, consisting of 3000-7000 amino acid residues, showed a similar amino acid composition, and they formed all the genes in the complete genome.