Cryptic Transcription and Early Termination in the Control of Gene Expression
Figure 2
Summary of regulatory mechanisms involving production of ncRNAs Transcription is depicted by dashed arrows, ncRNAs by red lines, and mRNAs by black lines. Transcription start sites (TSSs) are indicated by bent arrows. Red boxes indicate Nrd1-dependent termination signals. (a) Regulation by attenuation: a given transcription initiation event can give rise to either an unstable transcript generated by premature termination by the Nrd1 complex or a stable mRNA if transcription is allowed to reach the CPF-dependent terminator. (b) Regulation by transcriptional interference: transcription of a CUT (or a stable RNA) occludes the promoter of a downstream mRNA gene thus impairing pre-initiation complex assembly and subsequent expression of the gene. (c) Regulation by alternative TSS choice: transcription initiation can occur either at an upstream or a downstream TSS. When the upstream TSS is selected, Nrd1-dependent termination signals are included in the transcript, leading to transcription termination and production of a CUT. When transcription starts at the downstream TSSs, these signals are skipped and a functional mRNA is produced. Regulation occurs at the level of TSS selection. (d) Regulation by antisense transcription: antisense transcription impairs the sense of mRNA production without affecting the initiation step. (e) Regulation by antisense ncRNA: long ncRNAs are able to act in cis and in trans to recruit chromatin-modifying enzymes and silence the sense gene. In this case, regulation is mediated by the ncRNA.
