bacterial, archaeal and plant plastid code bacterial, archaeal and plant plastid code the bacterial, archaeal and plant plastid code (translation table 11) is the dna code used by bacteria, archaea, prokaryotic viruses and chloroplast proteins. it is essentially the same as the standard code, however there are some variations in alternative start codons. the code amino-acid biochemical properties nonpolar polar basic acidic termination: stop codon standard genetic code 1stbase 2nd base 3rdbase u c a g u uuu (phe/f) phenylalanine ucu (ser/s) serine uau (tyr/y) tyrosine ugu (cys/c) cysteine u uuc ucc uac ugc c uua (leu/l) leucine uca uaa stop (ochre) uga stop (opal) a uug ucg uag stop (amber) ugg (trp/w) tryptophan g c cuu ccu (pro/p) proline cau (his/h) histidine cgu (arg/r) arginine u cuc ccc cac cgc c cua cca caa (gln/q) glutamine cga a cug ccg cag cgg g a auu (ile/i) isoleucine acu (thr/t) threonine aau (asn/n) asparagine agu (ser/s) serine u auc acc aac agc c aua aca aaa (lys/k) lysine aga (arg/r) arginine a aug (met/m) methionine acg aag agg g g guu (val/v) valine gcu (ala/a) alanine gau (asp/d) aspartic acid ggu (gly/g) glycine u guc gcc gac ggc c gua gca gaa (glu/e) glutamic acid gga a gug gcg gag ggg g a the codon aug both codes for methionine and serves as an initiation site: the first aug in an mrna's coding region is where translation into protein begins. the other start codons listed by genbank are rare in eukaryotes and generally codes for met/fmet. b ^ ^ ^ the historical basis for designating the stop codons as amber, ochre and opal is described in an autobiography by sydney brenner and in a historical article by bob edgar. as in the standard code, initiation is most efficient at aug. in addition, gug and uug starts are documented in archaea and bacteria. in escherichia coli, uug is estimated to serve as initiator for about 3% of the bacterium's proteins. cug is known to function as an initiator for one plasmid-encoded protein (repa) in e. coli. in addition to the nug initiations, in rare cases bacteria can initiate translation from an auu codon as e.g. in the case of poly(a) polymerase pcnb and the infc gene that codes for translation initiation factor if3. the internal assignments are the same as in the standard code though uga codes at low efficiency for tryptophan in bacillus subtilis and, presumably, in escherichia coli.