An<unk>  or<unk>  is a portion of an organism's genome which contains a sequence of bases that could potentially encode a protein. The start and stop ends of the<unk>  are not equivalent to the ends of the mRNA, but they are usually contained within the mRNA.  In a gene,<unk> s are located between the start-code sequence (initiation codon) and  the stop-code sequence (termination codon). <unk> s are usually encountered when sifting through pieces of DNA while trying to locate a gene. Since there exist variations in the start-code sequence of organisms with altered genetic code, the<unk>  will be identified differently. A typical<unk>  finder will employ algorithms based on existing genetic codes (including the altered ones) and all possible<unk><unk> s.
In fact, the existence of an<unk> , especially a long one, is usually a good indication of the presence of a gene in the surrounding sequence.  In this case, the<unk>  is part of the sequence that will be translated by the ribosomes, it will be long, and if the DNA is eukaryotic, the<unk>  may continue over gaps called introns. However, short<unk> s can also occur by chance outside of genes.  Usually<unk> s outside genes are not very long and terminate after a few codons.
Once a gene has been sequenced it is important to determine the correct<unk>  <unk> . Theoretically, the DNA sequence can be read in six<unk><unk> s in organisms with double-stranded DNA; three in the forward and three in the reverse direction. The longest sequence without a stop codon usually determines the<unk> . That is the case with prokaryotes. Eukaryotic mRNA is typically monocistronic and therefore only contains a single<unk> .  A problem arises when working with eukaryotic pre-mRNA long parts of the DNA within an<unk>  are not translated (introns). When the aim is to find eukaryotic<unk> s it is necessary to have a look at the spliced messenger RNA mRNA.
For example, if you have 5'-UCUAAAGGUCCA-3' it has 2 out of 3<unk><unk> s possible.  This is one of the 2 possible mRNA sequences of the transcript, and we see that it can be<unk>  in the 3 possible ways:
1. UCU AAA GGU CCA
2. CUA AAG GUC etc
3. UAA AGG UCA etc
As you can see, the 3rd possibility has a stop codon, thus only 2 out of the 3<unk><unk> s are<unk>  (aka have no stop codons).
Open reading frame
DNA sequence
Short tandem repeat
DNA end
SI prefix
Triage tag
Locus 
DNA supercoil