Schematic illustration of the different classes of non-coding RNAs identified. Genes are depicted as thick arrows, with protein-coding genes shown in yellow and labeled as ‘ORF’s (open reading frame), non-coding RNAs shown in blue, and black depicting genes of either type. RNA transcripts are shown above their corresponding gene, with transcription initiating at the vertical line, and terminating at the small arrowhead. (A) Antisense RNAs (asRNAs) are expressed from a promoter on the strand opposite a protein-coding gene. (B) cutoRNAs occur when a long 3′ UTR of an mRNA overlaps with a downstream, convergently transcribed gene. The region of overlap is indicated with a bracketed line. (C) Small RNA (sRNA) genes are most commonly found in the intergenic region between genes, and typically target (by imperfect complementary base-pairing) one or more mRNAs expressed from disparate chromosomal locations.