Table 10.3 The standard genetic code Third First position Second position position (5′ end) (3′ end) U UU Phe E UCU Ser UAU Tyr v UGU Cys UUC Phe UCC Ser UUA Leu UCA Ser U A A Stop UGA Stop UAG Stop UGG Trp W G UU G LeuJ UCG Ser CUU Leu CCU Pro CAU His u CGU Arg CUC Leu CCC Pro p CAC His J CGC Arg CUA Leu CCA Pro CA A Gin CGA Arg CUG Leu CCG Pro U CA G GIn CGG Arg A UU Ile ACU Thr AAU Asn AGU Ser AUC Ile tI ACC Thr T A A C Asnj AGC Ser AUA Ile ACA Thr A A A Lys K AGA Arg R AUG Met M A C G Thr AA G Lys AGG Arg GUU Val GCU Ala GAU Asp GGU Gly GUC Val GCC Ala A G A C AspU G GC Gly G UA Val GCA Ala GAA Glu GGA Gly GUG Val J GCG Ala J G A G Glu G G G Gly Note: Each amino acid is given its conventional abbreviation in both the single-letter and the three-letter format. The codon AUG, which codes for me- thionine (boxed) is generally used for initiation. The codons are conventionally written with the 5′ base on the left and the 3′ base on the right.