Pyrimidine biosynthetic pathway of Baccillus subtilis

Abstract

Biochemical and genetic data were obtained from a series of 51 Pyr- strains of Bacillus subtilis. The observed enzymatic deficiencies allowed the mutants to be placed into 12 clases, some of which represent defects in more than one of the six known pyrimidine biosynthetic enzymes. Mapping analysis by transformation has shown that all the Pyr- mutations are located in a single small area of the B. subtilis genome. A correlation of the biochemical defects and the genetic data has been made. Those mutations conferring similar enzymatic deficiencies were found to be contiguous on the B. subtilis map. Regulatory aspects of the pyrimidine pathway have also been investigated and are compared to previously reported results from other organisms. Evidence is presented which bears upon the possible physical association of the first three enzymes and the association of at least some of the enzymes of this pathway with particulate elements of the cell. A model for the organization of the enzymes is presented with dihydroorotate dehydrogenase as the central enzyme in a proposed aggregate.

De novo synthesis of pyrimidine nucleotides by Helicobacter pylori

“…Activities of 32.8 nmol min-' mg-' protein have been reported for E. coli 15, R185482, a mutant which requires arginine and uracil for growth and appears to be blocked at carbamoyl phosphate synthesis (Taylor and Taylor 1964). Similarly, for S. marcescens strain HY (Wild and Belser 1977a,b), B. subtilis strain BK1 (Potvin and Kelleher 1975) and brewer's yeast (Liebermann et al 1955), activities of 36.3, 16.5 and 11.7 nmol min-' mg-' protein, respectively, have been reported. Although OPRTase and ODCase are different bacterial enzymes, in some micro-organisms such as certain yeast strains (Umezu et al 1971) and S .…”

Genetics and biochemistry of carbamoyl phosphate biosynthesis and its utilization in the pyrimidine biosynthetic pathway.

“…Also, some ACTmutants are also lacking CPS and DHO (EC 3.5.2.3). CPS, ACT, and DHO show similar but not identical molecular weights on a sucrose density gradient, with ACT slightly lighter and DHO slightly heavier than CPS, all three approximating 130,000 (121). These may of course be fragments resulting from dissociation or proteolysis of a larger, multifunctional complex.…”

“…However, more recently, both arginineand uracil-sensitive mutants have been isolated. The former class cotransforms with two pyrimidine auxotrophs, whereas the latter does not (120,121). It therefore would appear that there are two CPS enzymes in B. subtilis and that the carbamoyl phosphate synthesized is not efficiently channeled, since strains lacking one CPS are able to utilize carbamoyl phosphate from the other pathway.…”

Coordinate synthesis of the enzymes of pyrimidine biosynthesis in Bacillus subtilis.

“…The six enzymes of de novo pyrimidine biosynthesis are repressible by pyrimidines and coded for by adjacent genes in Bacillus subtilis (8), but it is not clear that synthesis of these enzymes is coordinately regulated. In the course of studies on the carbamyl phosphate synthetases of B. subtilis (6, 7), we found a simple means of isolating strains that are genetically derepressed for the enzymes of pyrimidine biosynthesis.…”