Open reading frame
In molecular genetics, an open reading frame (ORF) is the part of a reading frame that contains no stop codons. The transcription termination pause site is located after the ORF, beyond the translation stop codon, because if transcription were to cease before the stop codon, an incomplete protein would be made during translation.
One common use of open reading frames is as one piece of evidence to assist in gene prediction. Long ORFs are often used, along with other evidence, to initially identify candidate protein coding regions in a DNA sequence. The presence of an ORF does not necessarily mean that the region is ever translated. For example in a randomly generated DNA sequence with an equal percentage of each nucleotide, a stop-codon would be expected once every 21 codons. A simple gene prediction algorithm for prokaryotes might look for a start codon followed by an open reading frame that is long enough to encode a typical protein, where the codon usage of that region matches the frequency characteristic for the given organism's coding regions. By itself even a long open reading frame is not conclusive evidence for the presence of a gene.
If a portion of a genome has been sequenced (e.g. 5'-ATCTAAAATGGGTGCC-3'), ORFs can be located by examining each of the three possible reading frames on each strand. In this sequence two out of three possible reading frames are entirely open, meaning that they do not contain a stop codon:
- ...A TCT AAA ATG GGT GCC...
- ...AT CTA AAA TGG GTG CC...
- ...ATC TAA AAT GGG TGC C...
Possible stop codons in DNA are "TGA", "TAA" and "TAG". Thus, the last reading frame in this example contains a stop codon (TAA), unlike the first two.
ORF Finding Tools 
1.ORF Finder: The ORF Finder (Open Reading Frame Finder) is a graphical analysis tool which finds all open reading frames of a selectable minimum size in a user's sequence or in a sequence already in the database. This tool identifies all open reading frames using the standard or alternative genetic codes. The deduced amino acid sequence can be saved in various formats and searched against the sequence database using the WWW BLAST server. The ORF Finder should be helpful in preparing complete and accurate sequence submissions. It is also packaged with the Sequin sequence submission software.
2. ORF Investigator: ORF Investigator is a program which not only gives information about the coding and non coding sequences but also can perform pairwise global alignment of different gene/DNA regions sequences. The tool efficiently finds the ORFs for corresponding amino acid sequences and converts them into their single letter amino acid code, and provides their locations in the sequence. The pairwise global alignment between the sequences makes it convenient to detect the different mutations, including single nucleotide polymorphism. Needleman and Wunsch algorithms are used for the gene alignment. The ORF Investigator is written in the portable Perl programming language, and is therefore available to users of all common operating systems.
See also 
- Sequerome - A sequence profiling tool that links each BLAST record to the NCBI ORF enabling complete ORF analysis of a BLAST report.
- ORF Investigator ORF finding and Gene alignment program developed by Vivek Dhar Dwivedi and Sarad Kumar Mishra.
- Translation and Open Reading Frames
- NCBI ORF finder - A web based interactive tool for predicting and analysing ORFs from nucleotide sequences.
- ORF finder - A web based interactive tool for predicting and analysing ORFs from nucleotide sequences - hosted at bioinformatics.org
- hORFeome V5.1 - A web based interactive tool for CCSB Human ORFeome Collection
- ORF Marker - A free, fast and multi-platform desktop GUI tool for predicting and analyzing ORFs
- StarORF - A multi-platform, java based, GUI tool for predicting and analyzing ORFs and obtaining reverse complement sequence