Bifunctional protein PyrR <p>The PyrR protein from <taxon tax_id="1423">Bacillus subtilis</taxon> and many other bacteria is a bifunctional protein. Its primary function is the regulation of expression of pyrimidine biosynthetic (pyr) genes by binding to specific sites on pyr mRNA in a uridine nucleotide-dependent manner and altering the folding of downstream RNA to promote termination of transcription. PyrR also catalyzes the uracil phosphoribosyltransferase (UPRTase) reaction (<db_xref db="EC" dbkey="2.4.2.9"/>) even though it bears little amino acid sequence similarity to other bacterial UPRTases [<cite idref="PUB00053983"/>].</p>