Synthegradases are factors that enhance (or repress) both mRNA synthesis and decay. This double role is counterintuitive, and might seem cost ineffective. The gain in combining the processes of mRNA synthesis and decay is apparently in enabling rapid acquisition of a new steady-state level and better responsiveness to regulatory pathways
The mode of action of the synthegradase Rap1.
Right panel: Rap1 is recruited to ~5% of all yeast promoters (usually of highly transcribed genes) (see Lieb et al., 2001). Rap1 recruits an additional factor, whose identity is under investigation (black oval), that interacts with the RNA co-transcriptionally. This imprinting factor escorts the mRNA throughout its life and regulates its degradation. Left panel: promoters that do not recruit Rap1 give rise to transcripts that are not imprinted and therefore their decay in the cytoplasm is not regulated by mRNA imprinting. See graphical abstract.
The Implications:
- Promoters can recruit synthegradases, thereby affecting not only transcription but also the fate of their transcripts.
- Many promoter-binding proteins were classified as “transcription factors” based on the effect of their mutation/disruption on mRNA levels. Some of them might actually function as mRNA decay factors, or synthegradases – not genuine transcription factors.