Metabolism of pyrimidine deoxyribonucleosides in Neurospora crassa

Abstract

The experiments in this report involve the following series of reactions which were previously demonstrated with purified enzyme preparations from Neurospora crassa: thymidine a yields thymine ribonucleoside b yields thymine c yields 5-hydroxymethyluracil d yields 5-formyluracil e yields uracil-5-carboxylic acid f yields uracil. The evidence for some of the reactions occurring in vivo has been incomplete and for others totally lacking. In this paper intact cells of Neurospora are shown to be capable of converting the substrates of each of the reactions to the corresponding products. Studies are described which were carried out in vivo and in vitro with the pyrimidineless strains pyr-4,uc-1,uc-2 and pyr-4,uc-1,uc-3, developed by Williams and Mitchell. The results reported in the present paper indicate that (reaction a) and the uc-3 mutation affects thymine 7-hydroxylase (reactions c,d, and e). Evidence is presented for the 2'-hydroxylase reaction being the major, if not only, way by which Neurospora can initiate the conversion of thymidine to the pyrimidines of nucleic acids and for the 2'-hydroxylation of thymidine and deoxyuridine being catalyzed by the same enzyme. Deoxycytidine was shown not to be hydroxylated in intact cells but instead deaminated to deoxyuridine, which in turn was converted to uridine. Further studies with the uc-3-carrying strain showed that an enzyme other than thymine 7-hydroxylase can also convert 5-formyluracil to uracil-5-carboxylic acid.

Growth and differentiation of the water mold Blastocladiella emersonii: cytodifferentiation and the role of ribonucleic acid and protein synthesis.

“…In M. gypseum the early DNA synthesis was reportedly detected by thymidine incorporation and preceded a net increase in DNA content by 1 h, which would not be expected if the incorporation represented nuclear DNA replication. The general inability of "true" fungi to utilize thymidine directly for DNA synthesis (95,151,170) and the potential to convert it to other pyrimidines (209) suggest that these incorporation data need verification. Olson and Fuller (186) found the nuclear DNA content ofA.…”

Einbau von Thymidin in die DNS von Actinomyceten I. Der Einbau exogenen Thymidins in die DNS von Thermoactinomyces vulgaris

“…Dainit besteht bei Verwendung radioaktiv markierter Vorstufen die Moglichkeit, daB auDer DNS noch anderes Zellniaterial radioaktiv markiert wird (CLEAVER 1967, SHAFFER et al 1975. Fur eine Reihe von Bakterien ist bekannt, dalj ein Thymidinabbau verhindert werden kann, wenn der Desoxyribose-Pool erhoht (BOYCE u. SETLOW 1962) oder die enzymatische Aktivitat der Thymidinphosphorylase (EC 2.4.2.4) gehemmt wird (BUDMAN u. PARDEE 1967).…”

Regulation of thymidine metabolism in Neurospora crassa

“…N. crassa wild-type strain (1A) and the pyrimidineless mutant pyr-4 (which lacks orotidylate decarboxylase [28]) were obtained from the Fungal Genetics Stock Center, Arcata, Calif. The characterization and source of the triple mutant pyr-4,uc-1,uc-2 have been described (34,39). The double mutantpyr-4,uc-1 was isolated from a cross between strains 1A and pyr-4,uc-1,uc-2.…”

“…The double mutantpyr-4,uc-1 was isolated from a cross between strains 1A and pyr-4,uc-1,uc-2. This pyr-4,uc-1 strain was initially identified by its ability to utilize 1, 11. thymidine as a sole pyrimidine source, a by Williams and Mitchell (39), in cont pyrimidineless strains carrying the ucthat cannot effectively metabolize pyrim yribonucleosides (34). An additional st double mutant pyr-4,uc-1 was construct ing strains uc-1 and pyr-4.…”

“…In contrast to the incubause activity, tions in carboys, which were always carried out at 28 C, those in Erlenmeyer flasks were carried out at maintained 34 C unless otherwise indicated. nented with Pad-sections of mycelia were prepared and asestergaard-sayed as previously described (34). rowth tests.…”