IDENTIFICATION OF A NOVEL GENE OF PYRIMIDINE NUCLEOTIDE BIOSYNTHESIS,PYRDII, THAT IS REQUIRED FOR DIHYDROOROTATE DEHYDROGENASE-ACTIVITY INBACILLUS-SUBTILIS

An in-frame deletion in the coding region of a gene of previously unid entified function (which is called orf2 and which we propose to rename pyrDII) in the Bacillus subtilis pyr operon led to pyrimidine bradytr ophy, markedly reduced dihydroorotate dehydrogenase activity, and dere pressed levels of other enzymes of pyrimidine biosynthesis. The deleti on mutation was not corrected by a plasmid encoding pyrDI, the previou sly identified gene encoding dihydroorotate dehydrogenase, but was com plemented by a plasmid encoding pyrDII. We propose that pyrDII encodes a protein subunit of dihydroorotate dehydrogenase that catalyzes elec tron transfer from the pyrDI-encoded subunit to components of the elec tron transport chain.