FIG. 7. Model for new ORF evolution from intergenic transcripts. Shown is the potential mechanism for the evolution of new protein-encoding ORFs from intergenic transcripts. The process begins with adventitious transcription, followed by gain of a proper 3' end to allow for nuclear export, evolution of a start codon and engagement of the translation machinery, and natural selection of a desirable polypeptide. IT, intergenic transcript.