Phosphoribosyltransferase which catalyzes the formation of UMP from uracil in vitro and thus may be involved in UMP biosynthesis via the salvage pathway. May also participate in the first step of UMP synthesis by catalyzing the formation of orotidine 5'-phosphate, a UMP precursor, from orotate. diphosphate + orotidine 5'-phosphate = 5-phospho-alpha-D-ribose 1-diphosphate + orotate diphosphate + UMP = 5-phospho-alpha-D-ribose 1-diphosphate + uracil Pyrimidine metabolism; UMP biosynthesis via de novo pathway; UMP from orotate: step 1/2. Pyrimidine metabolism; UMP biosynthesis via salvage pathway; UMP from uracil: step 1/1. Homodimer. Expressed in body wall muscles, spermatheca and vulva muscles. Belongs to the purine/pyrimidine phosphoribosyltransferase family. PyrE subfamily.