Author/Editor		Aleksenko, Alexei; Liu, Wenguang; Gojković, Zoran; Nielsen, Jens; Piškur, Jure
Title		Structural and transcriptional analysis of the pyrABCN, pyrD and pyrF genes in Aspergillus nidulans and the evolutionary origin of fungal dihydroorotases
Type		članek
Source		Mol Microbiol
Vol. and No.		Letnik 33, št. 3
Publication year		1999
Volume		str. 599-611
Language		eng
Abstract		The six biochemical steps of the de novo pyrimidine biosynthesis pathway are conserved in all known organisms. However, in animals and fungi, unlike prokaryotes, at least the first two activities are grouped on a multifunctional enzyme. Here, we report cloning, mapping and transcriptional characterization of some pyrimidine biosynthesis genes in the filamentous fungus Aspergillus nidulans. The first two steps of the pathway are performed by a multifunctional enzyme comprising the activities of carbamoyl phosphate synthetase (CPSase) and aspartate transcarbamylase (ATCase). This polypeptide is encoded by a 7 kbp cluster gene, pyrABCN, which has a high degree of nucleotide identity with the Ura2 gene in Saccharomyces cerevisiae. The enzyme of the third step, dihydroorotase (DHOase), is encoded by a separate locus, pyrD. However, the pyrABCN gene apparently contains an evolutionary remnant of a DHOase-encoding sequence, similarly to the Ura2 gene of Saccharomyces cerevisiae. The pyrABCN gene is transcribed as a single 7 kb mRNA species. The level of transcripts of pyrABCN, pyrD and, to a lesser degree, pyrF genes responds to the presence of exogenous pyrimidines and to the conditions of pyrimidine starvation. Derepression of pyrABCN and pyrD under pyrimidine starvation is noticeably enhanced in pyrE mutants that accumulate dihydroorotic acid. The pyrABCN gene maps to the distal portion of the right arm of the chromosome VIII, whereas the pyrD gene, in contrast to early genetic data, is closely linked to the brlA gene and located to the right of it. Our data on mitotic recombination should help to verify the genetic map of the chromosome VIII. Comparison of amino acid sequences of active dihydroorotases with related enzymes and with their non-functional homologues in yeast and Aspergillus indicates that the active dihydroorotases from fungi are more similar to ureases and enzymes of the pyrimidine degradation pathway. (Abstract truncated at 2000 characters)
Descriptors		GENES, FUNGAL ASPARTATE CARBAMOYLTRANSFERASE ASPERGILLUS NIDULANS BASE SEQUENCE CHROMOSOME MAPPING CLONING, MOLECULAR DIHYDROOROTASE EVOLUTION, MOLECULAR GENE EXPRESSION REGULATION, ENZYMOLOGIC GENE EXPRESSION REGULATION, FUNGAL MOLECULAR SEQUENCE DATA MULTIENZYME COMPLEXES PHYLOGENY PYRIMIDINES RNA, MESSENGER RESTRICTION MAPPING SEQUENCE ALIGNMENT TRANSCRIPTION, GENETIC