Starting and stopping

The positions in the DNA sequence where transcription starts and stops are called the start codon and the stop codon. The sequence between these signaling codons is often called an open reading frame.

In most species, the ATG codon for methionine also signals the start of an open reading frame, while the stop codon may be one of TAA, TAG or TGA.

An example of a DNA sequence with a start (green) and stop (red) codon: