Читать книгу Snyder and Champness Molecular Genetics of Bacteria - Tina M. Henkin - Страница 192

During elongation, translation proceeds along the mRNA, one codon at a time, until the ribosome encounters one of three special codons, UAA, UAG, or UGA, that serve as translational stop signals. These codons, designated termination codons, stop codons, or nonsense codons (because they do not encode an amino acid), have no corresponding tRNA (Table 2.2). When a termination codon enters the A site of a translating ribosome, translation stops because no aa-tRNA can match the codon. Similar to the positioning of translation initiation codons, the termination codon that terminates translation may not be at the 3′ end of the mRNA molecule. The region between the termination codon and the 3′ end of the mRNA (or a downstream coding sequence for another polypeptide in a transcript that encodes multiple proteins [see below]) is called the 3′ untranslated region (3′-UTR).