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. 2015 Dec 23;6(2):435–446. doi: 10.1534/g3.115.023119

Figure 1.

Figure 1

Three classes of upstream open reading frames. The 5′ untranslated sequence (5UT) can contain no ATG in any frame (top), resulting in no upstream open reading frame (‘uORF’). It can contain one or more ATGs in frame with the main coding sequence (‘Reference CDS’), without an intervening stop codon (Class 1). Class 2 is the same as Class 1 but in a different reading frame; in general the Class 2 uORF will terminate shortly after entering the main CDS out-of-frame. Class 3 initiates (in any frame) and terminates within the 5UT. Note that I consider a maximum of one Class 1 and one Class 2 uORF per transcript, although these uORFs can contain internal ATGs that could in principle initiate a ‘different’ Class 1 or Class 2 uORF. A given transcript can (and frequently does) contain multiple Class 3 uORFs, in the same or different frames. I consider all of these as separate individuals.