The Enterococcus faecalis pyr operon is regulated by autogenous transcriptional attenuation at a single site in the 5 ' leader

The 5' end of the Enterococcus faecalis pyr operon specifies, in order, the promoter, a 5' untranslated leader, the pyrR gene encoding the regulatory protein for the operon, a 39-nucleotide (nt) intercistronic region, the pyr P gene encoding a uracil permease, a 13-nt intercistronic region, and the p yrB gene encoding aspartate transcarbamylase. The 5' leader RNA is capable of forming stem-loop structures involved in attenuation control of the oper on, No attenuation regions, such as those found in the Bacillus subtilis py r operon, are present in the pyrR-pyrP or pyrP-pyrB intercistronic regions. Several lines of evidence demonstrate that the E. faecalis pyr operon is r epressed by uracil via transcriptional attenuation at the single 5' leader termination site and that attenuation is mediated by the PyrR protein.