2021/2/21 1-1 polypeptide chains are specified by ORF 3 The protein coding region of each mRNa is composed of a contiguous, non-overlapping string of codons called an opening reading frame 名(ORF) a An orF should begins with a start codon and end with stop codon a mRNa containing more than one ORF is called polycistronic mRNAS 112021/2/21 11 1-1 polypeptide chains are specified by ORF ◼ The protein coding region of each mRNA is composed of a contiguous, non-overlapping string of codons called an opening reading frame (ORF) . ◼ An ORF should begins with a start codon and end with stop codon. ◼ mRNA containing more than one ORF is called polycistronic mRNAs. Message RNA