The ‘reading’ of bases in messenger RNA (or deduced from DNA) according to their correct triplet combinations for each coding unit (codon) of the genetic code. Hence, the reading frame is established according to precisely where translation starts. For example, if translation starts one base either side of the correct base, an entirely different sequence of codons will be read, resulting in a faulty polypeptide or none at all. The hallmark of a functional gene is that it is transcribed to produce an open reading frame (ORF), consisting of a start codon to pinpoint exactly where translation should start, a stop codon to signal termination of translation, and typically a long sequence of codons that specify the constituent amino acids of the polypeptide (as well as introns in most eukaryote genes).