<P> The start codon is the first codon of a messenger RNA (mRNA) transcript translated by a ribosome . The start codon always codes for methionine in eukaryotes and a modified Met (fMet) in prokaryotes . The most common start codon is AUG . </P> <P> The start codon is often preceded by a 5' untranslated region (5' UTR). In prokaryotes this includes the ribosome binding site . </P> <P> Alternative start codons are different from the standard AUG codon and are found in both prokaryotes (bacteria) and eukaryotes . Alternate start codons are still translated as Met when they are at the start of a protein (even if the codon encodes a different amino acid otherwise). This is because a separate transfer RNA (tRNA) is used for initiation . </P>

How many start codons are in the genetic code