SEQUENCE-ANALYSIS AND IDENTIFICATION OF THE PYRKDBF OPERON FROM LACTOCOCCUS-LACTIS INCLUDING A NOVEL GENE, PYRK, INVOLVED IN PYRIMIDINE BIOSYNTHESIS

Three genes encoding enzymes involved in the biosynthesis of pyrimidin es have been found to constitute an operon in Lactococcus lactis. Two of the genes are the well-known pyr genes pyrDb and pyrF, encoding dih ydroorotate dehydrogenase and orotidine monophosphate decarboxylase, r espectively. The third gene encodes a protein which was shown to be ne cessary for the activity of the pyrDb-encoded dihydroorotate dehydroge nase; we propose to name the gene pyrK. The pyrK-encoded protein is ho mologous to a number of proteins which are involved in electron transf er. The lactococcal pyrKDbF operon is highly homologous to the corresp onding part of the much-larger pyr operon of Bacillus subtilis, orf2, the pyrK homolog in B, subtilis, has also been shown to be necessary f or pyrimidine biosynthesis (A, E, Kahler and R. L. Switzer, J, Bacteri ol, 178:5013-5016, 1996). Four genes adjacent to the operon, i.e., orf E, orfA, orfC, and gidB, were also sequenced. Three of these were excl uded as members of the pyr operon by insertional analysis (orfA) or by their opposite direction of transcription (orfE and gidB), orfC, howe ver, seems to be the distal gene in the pyrKDbF-orfC operon.