Using site-directed mutagenesis, arginine codons 206 and 210 in exon 4 were changed to lysine codons (p.R206K, p.R210K). A puromycin resistance gene cassette was inserted downstream of the targeted codons in exon 4. The two targeted arginines are normally methylated as part of the regulation of the peptide's activity; lysines cannot be methylated. (J:281491)