Pathways of Pyrimidine Salvage in Streptomyces

Abstract

Using 5-fluoropyrimidine analogues, high-performance liquid chromatography (HPLC), and the feeding of pyrimidine compounds to pyrimidine auxotrophs, the pathways for salvage of exogenous pyrimidine nucleosides and bases in Streptomyces were established. Selection for resistance to the analogues resulted in the isolation of strains of S. griseus lacking the following enzyme activities: uracil phosphoribosyltransferase (upp) and cytidine deaminase (cdd). The conversion of substrates in the pathway was followed using reverse-phase HPLC. The strains deficient in salvage enzymes were also verified by this method. In addition, feeding of exogenous pyrimidines to strains lacking the biosynthetic pathway confirmed the salvage pathway. Data from the analogue, HPLC, and feeding experiments showed that Streptomyces recycles the pyrimidine base uracil, as well as the nucleosides uridine and cytidine. Cytosine is not recycled due to a lack of cytosine deaminase.

Aquifex aeolicus Dihydroorotase

“…A plausible hypothesis is that the association with ATCase displaces the loop rendering the A. aeolicus DHOase active site accessible. This sort of functional interaction between DHOase and ATCase has not been previously observed and it is not known whether a similar switch mechanism occurs in the 450 -500-kDa duodecameric complex of other type IC enzymes (38). Interestingly, there is evidence that the association of the inactive pseudo-DHOase homolog with ATCase in P. putida (20) and P. aerugenosis (19,20) may be necessary to preserve the ATCase activity.…”

“…The mammalian CAD DHOase domain and the A. aeolicus DHOase are classified as type I, whereas the E. coli enzyme is type II. Whereas it will be necessary to examine more of these proteins before a definitive (38). Thus far, the enzymes from 22 organisms have been assigned as type IA enzymes although only a few have been biochemically characterized, so it is possible that other enzymes in this subgroup will also have to be reclassified.…”

A Member of the Second Carbohydrate Uptake Subfamily of ATP-Binding Cassette Transporters Is Responsible for Ribonucleoside Uptake inStreptococcus mutans

“…5-Fluoropyrimidine analogues are powerful reagents for analyzing pyrimidine metabolism (13,17). To inhibit growth, 5-fluorocytidine and 5-fluorouridine, toxic ribonucleoside derivatives, must be taken into the bacterium and converted by salvage enzymes to the corresponding nucleotides (21).…”

“…Inactivation of the genes encoding the ATPase or the solute binding protein resulted in strains that were less susceptible to the toxic ribonucleosides 5-fluorocytidine and 5-fluorouridine. Furthermore, these strains had considerably reduced rates of [2-14 C]cytidine, [2-14 C]uridine, and [8][9][10][11][12][13][14] C]adenosine uptake. The broad range of substrates that inhibit 5-flurocytidine and 5-flurouridine toxicity and [2-14 C]cytidine uptake indicates that RnsBACD can transport most ribonucleosides, including 2-deoxyribonucleosides.…”

Uracil Salvage Pathway in Lactobacillus plantarum : Transcription and Genetic Studies

“…This genetic organization is different from previously studied organisms: the upp and uraA genes are unlinked in Streptomyces (GenBank accession no. NC_003888) (13) and form a bicistronic operon in Escherichia coli (1), while the pyrP gene is cotranscribed with the adjacent pyrR/pyrB genes in B. subtilis (32) and L. lactis (18). In these organisms, pyrP transcription is regulated in response to pyrimidine availability.…”