PyrC leader

In molecular biology, the PyrC leader is a cis-regulatory RNA element found at the 5' of the PyrC mRNA in Enterobacteria. The PyrC gene encodes Dihydroorotase, an enzyme involved in pyrimidine biosynthesis.^[1] The PyrC leader regulates expression of PyrC. Translation initiation can occur at four different sites within this leader sequence, under high CTP conditions the translation initiation site is upstream of that used under low CTP conditions, additional cytosine residues are incorporated into the mRNA resulting in the formation of an RNA hairpin. This hairpin blocks ribosome-binding at the Shine-Dalgarno sequence, and therefore blocks expression of PyrC. Under low CTP conditions the initiation site is further downstream and does not result in hairpin formation, so the ribosome can bind to the Shine-Dalgarno sequence and PyrC is expressed.^[2]

Further reading

• Liu, J; Turnbough CL, Jr (May 1994). "Effects of transcriptional start site sequence and position on nucleotide-sensitive selection of alternative start sites at the pyrC promoter in Escherichia coli". Journal of Bacteriology. 176 (10): 2938–2945. PMC 205450. PMID 7910603.
• Wilson, HR; Archer, CD; Liu, JK; Turnbough CL, Jr (January 1992). "Translational control of pyrC expression mediated by nucleotide-sensitive selection of transcriptional start sites in Escherichia coli". Journal of Bacteriology. 174 (2): 514–524. PMC 205745. PMID 1345912.