Open reading frame

An open reading frame or ORF is any sequence of DNA or RNA that can be translated into a protein. In a gene, ORFs are located between the start-code sequence (initiation codon) and the stop-code sequence (termination codon). ORFs are usually encountered when sifting through pieces of DNA while trying to locate a gene. In fact, the existence of an ORF, especially a long one, is usually a good indication of the presence of gene in the surrounding sequence. In this case, the ORF is part of the sequence that will be translated by the ribosomes and the ORF will be long and continue over gaps, or introns. However, short ORFs can also occur by chance outside of genes. ORFs outside of genes are not very long and tend to terminate rapidly i.e. after a few codons.