Figure 1. Examples of pervasive bidirectional transcription.

A) Transcription at a bidirectional promoter involves pairs of protein-coding transcripts, pairs of non-coding transcripts, or coding and non-coding transcripts. The dark blue boxes represent protein-coding genes. B) Schematic examples of non-coding RNAs in proximity to protein-coding genes reported in diverse studies and organisms. The black bars represent proteincoding transcripts and the arrowheads the direction of transcription. The narrow arrows represent long stable transcripts (green), short stable transcripts (yellow), unstable transcripts (dashed gray), nascent RNAs (turquoise) and actively transcribed RNAs (blue). As indicated by arrow directions, non-coding RNAs can be generated from either strand relative to the coding transcript. Different types of ncRNA transcription are circled and shown on different protein-coding transcripts. The background shading indicates species where transcripts were defined. See Table 1 for details. Transcripts are represented as described in different studies; note that in reality, some may be the same non-coding transcript but profiled with a different technique (see text for discussion). Note also that the lengths of noncoding RNAs are often not precisely known and are not represented here in accurate proportion to protein-coding gene lengths.