Figure 4

Transcription of lncRNA creates permissive chromatin environment. (a) Top left: an inactive enhancer with closed chromatin cannot activate the pc gene. Top right, bottom left: transcription of the enhancer opens chromatin. Bottom right: open chromatin at the enhancer allows TF binding and interaction with and activation of the pc gene promoter. (b) VDJ recombination. From top to bottom: 1, D and J segments are joined and the V region has closed chromatin; 2, antisense transcription through the V region opens the chromatin and allows recombination factors to bind; 3, a V segment is joined to the DJ segment. (c) Top: at a bidirectional promoter a lncRNA and a pc gene are transcribed in opposite directions. The promoter is always in an open chromatin conformation as either the lncRNA or the pc gene is transcribed, which is thought to reduce transcriptional noise. Bottom: a unidirectional pc gene promoter can acquire a closed chromatin conformation due to stochastic TF binding, which is thought to increase transcriptional noise. Noise defines the variation of expression of a transcript between genetically identical cells caused by the stochastic binding of TFs regulated by the local chromatin environment. For details see Figure 1g, Figure 2d, Figure 3c and text.