Figure 2.

Proposed smORF classification. (A) smORF classes and their representative locations. Hundreds of thousands of smORFs in the genome are non-expressed and are therefore classified as intergenic smORFs (green box). Expressed smORFs are classified as genic smORFs (green box) and are subdivided into smORFs located in non-coding RNAs (ncRNAs) (red box) and smORFs located in canonical mRNAs (blue box). Different types of ncRNAs and canonical mRNAs with their respective classes of smORFs are represented in red and blue boxes. Red tracks represent intergenic smORFs; blue tracks represent genic smORFs; yellow tracks represent large ORFs. (B) smORF classification chain. SmORF classes can be organized into groups and subgroups defined by transcriptional features.