Final answer:
RNA leader sequences can form secondary structures called attenuators, leading to the premature termination of mRNA transcription. Attenuators control gene expression by determining the formation of stem-loop structures that either terminate or allow the transcription process to continue.
Step-by-step explanation:
RNA leader sequences can form secondary structures called attenuators. These structures can terminate transcription of the rest of the mRNA prematurely. Attenuation is a regulatory mechanism whereby secondary stem-loop structures formed within the 5' end of an mRNA being transcribed determine the fate of transcription and translation. In E. coli, for example, the trp operon contains a leader sequence with regions that can base pair in different configurations, leading to the formation of either a terminator stem-loop or an antiterminator stem-loop. The terminator stem-loop causes transcription to terminate by releasing RNA polymerase from the mRNA. In contrast, an antiterminator stem-loop prevents the formation of the terminator stem-loop, allowing RNA polymerase to transcribe structural genes.
Rho-independent termination is another example where a hairpin loop structure within the mRNA induces the dissociation of RNA polymerase and the termination of transcription. Similarly, riboswitches and microRNAs can influence mRNA stability and regulate gene expression by interacting with secondary structures within the RNA molecule.