Activation Control of purDEK and purC Gene Expression in Lactococcus lactis

A comparison of the purC and purD upstream regions from Lactococcus lactis revealed the presence of a conserved ACCGAACAAT decanucleotide sequence located precisely between -79 and –70 nucleotides upstream from the transcriptional start sites. Both promoters have well defined -10 regions but lack sequences resembling -35 regions for 70 promoters . Fusion studies point to the importance of the conserved sequences in purine mediated regulation. Adjacent to the conserved sequence in purC is a second and similar region required for high expression of the gene. A consensus “PurBox” sequence (AWWWCCGAACWWT) could be proposed for the three regions. By site directed mutagenesis we have found that mutation of the central G’s in the PurBox sequences to C residues results in low residual transcription and the loss of purine mediated regulation at the purC and purD promoters. The deletion analysis also showed that the nucleotides before the central CCGAAC core in the PurBox are of importance. All results support the idea that purC and purD transcription is regulated by a transcriptional activator, binding to the PurBox sequences.