Translational regulation in prokaryotes ensures efficient protein synthesis by controlling ribosome access to mRNA. This regulation is mediated by secondary RNA structures, including translational riboswitches, RNA thermometers, and small RNAs (sRNAs), which respond to intracellular and environmental signals to modulate gene expression.
Riboswitches in the leader region of mRNAs can regulate translation by altering the accessibility of the Shine-Dalgarno (SD) sequence, which is essential for ribosome binding. Effector molecules bind to riboswitches, inducing conformational changes that either expose or mask the SD sequence:
This regulatory mechanism allows bacteria to control protein synthesis based on metabolite availability, optimizing energy expenditure.
Pathogenic bacteria utilize RNA thermometers to regulate gene expression in response to temperature shifts. These temperature-sensitive RNA elements, located in the 5' untranslated regions (UTRs) of specific mRNAs, modulate translation by altering the SD sequence's accessibility:
This mechanism enables bacterial pathogens to express virulence factors preferentially at host body temperatures.
Small RNAs (sRNAs) regulate translation by interacting with target mRNAs to either repress or enhance translation. Their function depends on whether they act in cis or trans:
sRNAs can either inhibit translation by blocking the ribosome-binding site or enhance translation by disrupting inhibitory RNA structures, thereby exposing the SD sequence.
By modulating translation through riboswitches, RNA thermometers, and sRNAs, bacteria efficiently control protein synthesis in response to metabolic cues, environmental temperature, and stress conditions. This dynamic regulation conserves cellular resources and enhances bacterial adaptability in diverse and fluctuating environments.
Riboswitches, RNA thermometers, small RNAs, or sRNAs are secondary RNA structures that regulate translation.
Translational riboswitches utilize effector molecules that bind to the mRNA leader regions, exposing or masking the Shine-Dalgarno, or SD, sequence.
When exposed, the 30S ribosomal subunit binds to the SD sequence to initiate translation. Conversely, masking prevents ribosome binding, halting translation.
Besides effectors, environmental temperature also toggles gene expression in certain microorganisms.
RNA thermometers are temperature-sensitive regulatory elements in the leader regions of certain mRNAs.
At low temperatures, RNA thermometers form stable stem-loop structures that base-pair with theSD sequence, masking it from ribosomes.
Higher temperatures destabilize these structures, exposing the SD sequence for translation.
sRNAs bind target mRNAs to either block ribosome access or facilitate translation.
Cis-acting sRNAs influence a single gene by complementing its target mRNA. Meanwhile, chaperone-assisted trans-acting sRNAs regulate multiple genes by binding to short complementary targets.
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