The Codons with dual functions areI. AUG  II. GUG III. UAG  IV. UGG

The codon AUG can act as initiating codon as well as interstitial codon. As initiating codon, it indicates amino acid methionine in eukaryotes and formyl methionine in prokaryotes. As interstitial codon it indicates methionine in both Prokaryotes and Eukaryotes. GUG acts as initiating codon in some prokaryotic mRNAs and indicates formyl methionine and as subsequent codon it indicates amino acid Valine. It indicates only Valine in Eukaryotes. UAG is non-sense codon and does not indicate any amino acid. UGG indicates only the amino acid Tryptophan.