Regulates transcriptional attenuation of the pyrimidine nucleotide (pyr) operon by binding in a uridine-dependent manner to specific sites on pyr mRNA. This disrupts an antiterminator hairpin in the RNA and favors formation of a downstream transcription terminator, leading to a reduced expression of downstream genes. Also displays a weak uracil phosphoribosyltransferase activity which is not physiologically significant. diphosphate + UMP = 5-phospho-alpha-D-ribose 1-diphosphate + uracil Optimum pH is 8.2 for UPRTase activity. Homodimer and homohexamer; in equilibrium. Mutagenesis studies identified four amino acid residues that seem to be involved directly in binding of the protein to pyr mRNA: Thr-18, His-22, Arg-141 and Arg-146. Arg-27 and Lys-152 were also likely to be involved in RNA-binding, but mutations may have altered their subunit-subunit interactions. Arg-19 was implicated in pyr regulation, but a specific role in RNA-binding could not be demonstrated. UMP and UTP increase the affinity of PyrR for RNA. Belongs to the purine/pyrimidine phosphoribosyltransferase family. PyrR subfamily.