Molecular characterization of ubiquitin genes from Aspergillus nidulans : mRNA expression on di¡erent stress and growth conditions Maria Anto ª nia Noventa-Jorda ¬o a , Adriana Mendes do Nascimento a , Maria Helena S. Goldman b , Hector F. Terenzi b , Gustavo H. Goldman a ; * a Departamento de Cie ªncias Farmace ªuticas, Faculdade de Cie ªncias Farmace ªuticas de Ribeira ¬o Preto, Universidade de Sa ¬o Paulo, Av. do Cafe ¨ S/N, CEP 14040-903, Ribeira ¬o Preto, Universidade de Franca, Sa ¬o Paulo, Brazil b Faculdade de Filoso¢a, Cie ªncias e Letras de Ribeira ¬o Preto, Universidade de Sa ¬o Paulo, Sa ¬o Paulo, Brazil Received 16 August 1999; received in revised form 15 November 1999; accepted 13 December 1999 Abstract We are interested in studying the ubiquitin (UBI) gene expression during different stress and growth conditions in the filamentous fungus Aspergillus nidulans. Here, we report the cloning of a cDNA clone that corresponds to a gene, ubi1, that encodes a carboxyl extension protein from A. nidulans. This cDNA corresponds to a gene that encodes a protein that showed high homology to other polyubiquitin and CEP-80 genes at the N- and C-terminus, respectively. We characterize the mRNA expression of the CEP and polyubiquitin genes during several growth and stress conditions. Expression of the ubi1 and ubi4 genes was correlated with cell growth in most of the carbon sources used, except maltose. Both ubi1 and ubi4 genes were induced upon heat-shock, although the levels of expression were raised quicker for ubi4 than for ubi1. The ubi1 and ubi4 genes displayed a very complex expression pattern in presence of drugs with a different mechanism of action suggesting that the regulatory processes controlling UBI gene expression discriminate between different stresses and can affect individually each UBI gene. The ubi1 gene was highly expressed in presence of hydrogen peroxide while the ubi4 mRNA level was not affected; several metals in our experimental conditions were not able to induce either ubi1 nor ubi4 genes. ß 2000 Elsevier Science B.V. All rights reserved. Keywords : Ubiquitin ; Ubiquitin extension protein ; Stress tolerance ; Aspergillus nidulans 1. Introduction Ubiquitin (UBI) is a highly conserved 76 amino acid protein found in all eukaryotic organisms that plays an essential role in intracellular turnover of proteins [1^7]. The covalent ligation of UBI to var- ious acceptor proteins in eukaryotic cells participates in or regulates a number of cellular processes, such as selective protein degradation, DNA repair, pro- gression through the cell cycle, signal transduction, transcriptional regulation, the nuclear transport pro- cess, receptor control by endocytosis, the processing of antigens in the immune system, pathological alter- ations and programmed cell death [3,4,8,9]. A major function of UBI is to label proteins destined for se- lective elimination. UBI-encoding sequences can be divided into two groups. The polyubiquitin gene en- codes a protein containing tandem head-to-tail re- peats of the monomeric UBI sequence. This protein is then processed by de-ubiquitinating enzymes to 0167-4781 / 00 / $ ^ see front matter ß 2000 Elsevier Science B.V. All rights reserved. PII:S0167-4781(99)00242-0 * Corresponding author. Fax: +55 (16) 6331092/6024280; E-mail : ggoldman@usp.br Biochimica et Biophysica Acta 1490 (2000) 237^244 www.elsevier.com/locate/bba