Author/Editor		Piškur, Jure; Kolbak, Dorthe; Sondergaard, Leif; Pedersen, Mogens B
Title		The dominant mutation Suppressor of black indicates that de novo pyrimidine biosynthesis is involved in the Drosophila tan pigmentation pathway
Type		članek
Source		Mol Gen Genet
Vol. and No.		Letnik 241, št. 3-4
Publication year		1993
Volume		str. 335-40
Language		eng
Abstract		A deficiency in the production of beta-alanine causes the black (b) phenotype of Drosophila melanogaster. This phenotype is normalized by a semi-dominant mutant gene Su(b) shown previously to be located adjacent to or within the rudimentary (r) locus. The r gene codes for three enzyme activities involved in de novo pyrimidine biosynthesis. Pyrimidines are known to give rise to beta-alanine. However, until recently it has been unclear whether de novo pyrimidine biosynthesis is directly coupled to beta-alanine synthesis during the tanning process. In this report we show that flies carrying Su(b) can exhibit an additional phenotype, resistance to toxic pyrimidine analogs (5-fluorouracil, 6-azathymine and 6-azauracil). Our interpretation of this observation is that the pyrimidine pool is elevated in the mutant flies. However, enzyme assays indicate that r enzyme activities are not increased in Su(b) flies. Genetic mapping of the Su(b) gene now places the mutation within the r gene, possibly in the carbamyl phosphate synthetase (CPSase) domain. The kinetics of CPSase activity in crude extracts has been studied in the presence of uridine triphosphate (UTP). While CPSase from wild-type flies was strongly inhibited by the end-product, UTP, CPSase from Su(b) was inhibited to a lesser extent. We propose that diminished end-product inhibition of de novo pyrimidine biosynthesis in Su(b) flies increases available pyrimidine and consequently the beta-alanine pool. Normalization of the black phenotype results.
Descriptors		SUPPRESSION, GENETIC ANIMALS ASPARTATE CARBAMOYLTRANSFERASE COLOR DIHYDROOROTASE DROSOPHILA GENES, DOMINANT PHENOTYPE PYRIMIDINES BETA-ALANINE