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. Author manuscript; available in PMC: 2021 Oct 7.
Published in final edited form as: Cell Rep Methods. 2021 Sep 16;1(5):100081. doi: 10.1016/j.crmeth.2021.100081

Figure 1. Effects of TSS selection on gene expression.

Figure 1.

(A) Possible effects of 5′ TL lengthening on transcript stability and translation. Transcription factor (TF) 1 specifies use of a proximal promoter, leading to a transcript with a short 5′ TL, while TF2 activates an upstream promoter that produces a transcript with a long 5′ TL. The extended 5′ TL may contain a uORF, which can act as a “sponge” for ribosomes by preventing them from reaching the transcript’s primary ORF and may also lead to destruction of the transcript via NMD if the uORF stop codon is recognized as premature. The 5′ TL may also contain an IRES, enabling cap-independent translation. We note that these 5′ TL features are not mutually exclusive and direct interested readers to a recent comprehensive review on the roles of 5′ TLs in gene regulation (Leppek et al., 2018).

(B) Production of transcripts encoding distinct protein isoforms by TF-mediated activation of alternative promoters.