sconC , a gene involved in the regulation of sulphur metabolism in Aspergillus nidulans , belongs to the SKP1 gene famil
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ORIGINAL PAPER
M. Piotrowska á R. Nator á A. Paszewski
sconC, a gene involved in the regulation of sulphur metabolism in Aspergillus nidulans, belongs to the SKP1 gene family Received: 20 February 1999 / Accepted: 30 June 2000 / Published online: 10 August 2000 Ó Springer-Verlag 2000
Abstract sconC, which encodes a negative regulator of sulphur metabolism in Aspergillus nidulans was cloned, sequenced, and found to belong to the highly conserved family of SKP1 genes essential for many cell functions, including cell cycle regulation. The ORF of 722 bp, encoding a protein of 161 amino acids, is interrupted by four introns. There is a ®fth intron (135 bp long) in the upstream untranslated sequence. Two point mutations in conserved regions were identi®ed in the mutant alleles sconC3 and sconC1, which result in relief of sulphur metabolite repression. The SCONC protein contains the PEST sequence common for proteins that are subject to rapid turnover. Transformation of the sconC3 mutant with sconB+ restores the wild-type phenotype. The sconB gene encodes a protein containing the F-box, a domain known to interact with Skp1 proteins. By analogy with other systems, it seems likely that the SCONC protein interacts with SCONB. sconC mRNA is present in the sconC3 and sconB2 mutants and the level of the sconC transcript seems not to be signi®cantly regulated by supplementation of the medium with sulphur. Key words sconC á Skp1 á Aspergillus nidulans á SCF complex á Sulphur regulation
Introduction Aspergillus nidulans, like other fungi, possesses a regulatory system known as sulphur metabolite repression which controls the expression of several coordinately
Communicated by C. A. M. J. J. van den Hondel M. Piotrowska á R. Nator á A. Paszewski (&) Institute of Biochemistry and Biophysics, Polish Academy of Sciences, 5A PawinÄskiego St., 02-106 Warsaw, Poland E-mail: [email protected] Fax: +48-39-121623
regulated genes involved in sulphur utilisation. These include the genes encoding some of the enzymes of the sulphate assimilation pathway, sulphohydrolases and homocysteine synthase, the ®rst enzyme of the alternative pathway for cysteine synthesis (Fig. 1). Repression of these genes takes place under high-sulphur conditions and is especially strong when organic sulphur compounds (such as methionine), which are the preferred sources, are available (Paszewski and Grabski 1974, 1975). Four negatively acting regulatory genes, sconA, B, C and D, that control sulphur metabolism in A. nidulans have been identi®ed and mapped in this laboratory (Nator et al. 1993). Mutations in scon genes relieve sulphur metabolite repression, leading to constitutive synthesis of several enzymes of sulphur metabolism, including sulphate permease. In consequence, scon mutants, unlike the wild type, are sensitive to selenate, a toxic analogue of sulphate, even in the presence of methionine (Arst 1968; Nator et al. 1998). Besides this, scon mutations suppress lesions in the pathway leading from cysteine to homocysteine by causing derepression of
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