Yeast Yeast 2004; 21: 211–218. Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/yea.1066 Yeast Sequencing Report Cloning and expression analysis of the ornithine decarboxylase gene (PbrODC) of the pathogenic fungus Paracoccidioides brasiliensis Gustavo A. Ni˜ no-Vega 1 *, Fran¸ coise Sorais 1 , Ana-Mar´ ıa Calcagno 1 , Jos´ e Ruiz-Herrera 2 , Alfredo D. Mart´ ınez-Espinoza 2# and Gioconda San-Blas 1 1 Instituto Venezolano de Investigaciones Cient´ ıficas, Centro de Microbiolog´ ı a y Biolog´ ı a Celular, Apartado 21827, Caracas 1020A, Venezuela 2 Centro de Investigaci´ on y de Estudios Avanzados del IPN, Departamento de Ingenier´ ıa Gen´ etica, Unidad Irapuato, Irapuato, Gto, Mexico *Correspondence to: Gustavo A. Ni˜ no-Vega, Instituto Venezolano de Investigaciones Cient´ ıficas, Centro de Microbiolog´ ıa y Biolog´ ıa Celular, Apartado 21827, Caracas 1020A, Venezuela. E-mail: gnino@ivic.ve # Present address: Department of Plan Pathology, University of Georgia, Griffin Campus 1109 Experiment St., Griffin, GA, 30223-1797, USA. Received: 25 May 2003 Accepted: 16 October 2003 Abstract We describe the isolation and sequencing of PbrODC, the gene encoding ornithine decarboxylase (ODC) in Paracoccidioides brasiliensis. The gene contains a single open reading frame made of 1413 bp with a single intron (72 bp), and encodes a 447 amino acid polypeptide with a predicted molecular weight of 50.0 kDa, an isoelectric point of 4.9 and a high similarity to other fungal ornithine decarboxylases. Functionality of the gene was demonstrated by transformation into a Saccharomyces cerevisiae odc null mutant. A phylogenetic tree generated with several fungal ODCs provided additional evidence to favour a taxonomic position for P. brasiliensis as an ascomycetous fungus, belonging to the order Onygenales. Expression of the PbrODC gene was determined by Northern analyses during growth of the mycelial and yeast forms, and through the temperature-regulated dimorphic transition between these two extreme phases. Expression of PbrODC remained constant at all stages of the fungal growth, and did not correlate with a previously observed increase in the activity of ornithine decarboxylase at the onset of the budding process in both yeast growth and mycelium-to-yeast transition. Accordingly, post-transcriptional regulation for the product of PbrODC is suggested. The PbrODC gene sequence is available at the GenBank database under Accession No. AF212867. Copyright  2004 John Wiley & Sons, Ltd. Keywords: Paracoccidioides brasiliensis ; polyamines; gene expression; dimorphic transition; taxonomy; Onygenales Introduction Polyamine metabolism is known to play a key role in differentiation of dimorphic fungi, par- ticularly during the process of dimorphic transi- tion (Calvo-M´ endez et al., 1987; Inderlied et al., 1980; Mart´ ınez-Pacheco et al., 1989; Ruiz-Herrera, 1994). The first step on the biosynthesis of polyamines is the decarboxylation of ornithine by ornithine decarboxylase (ODC) to form putrescine, one of the most highly regulated enzymatic reac- tions in eukaryotic systems (Tabor and Tabor, 1984). In dimorphic fungi, morphological changes are expressed mainly in a rapid transition between yeasts and hyphal forms. This event is accom- panied by an increase in ODC activity, primar- ily during the early stages of mycelial formation, such as occurs in the Mucorales (Calvo-M´ endez et al., 1987; Mart´ ınez-Pacheco et al., 1989; Reyna- L´ opez and Ruiz-Herrera, 1993), Yarrowia lipolytica (Guevara-Olvera et al., 1993; Jim´ enez-Bremont et al., 2001) and Candida albicans (L´ opez et al., 1997). However, in Paracoccidioides brasiliensis, a dimorphic fungus responsible for one of the most frequent mycoses in the rural population of Central Copyright  2004 John Wiley & Sons, Ltd.