Tel: +81862518712. Abstract: Nucleotide and amino acid sequences at the N-terminus affect the expression level and cytotoxicity of proteins; however, their effects are not fully understood yet. Here, N-terminal 30 nucleotide/10 amino acid (N10) sequences that affect the expression level and cytotoxicity of a green fluorescent protein were systematically isolated in the budding yeast Saccharomyces cerevisiae. The expression per gene (EPG) and gene copy number limit (CNL) relationships were

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... ed to assess the effects of the N10 sequence. The isolated N10 nucleotide sequences suggested that codon optimality is the major determinant of the protein expression level. A higher number of hydrophobic or cysteine residues in the N10 sequence seemed to increase the cytotoxicity of the protein. Therefore, a high frequency of specific amino acid residues in the outside of the main tertiary structure of proteins might not be preferable.