Polyamines are required for cellular growth and differentiation. In mammals and fungi they are synthesized via a pathway involving ornithine decarboxylase (ODC), which transforms ornithine into putrescine. We have cloned and disrupted the gene coding for ODC in Yarrowia lipolytica to analyze the role of polyamines in dimorphism of this fungus. Substrate- and cofactor-binding motifs, as well as two putative PEST boxes were identified in the amino acid sequence. A single transcript 1.7 kb in size was identified by Northern hybridization, and confirmed by rapid amplification of cDNA ends (RACE). Null mutants lacked ODC activity and behaved as polyamine auxotrophs. When low levels of polyamines were supplied to the null mutant, only yeast-like, but not mycelial growth was sustained. This phenomenon was confirmed by introduction of the YlODC gene under the control of an inducible promoter into the null mutant. © 2001 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.

This work was partially supported by CONACYT, Mexico, DGICYT and the Junta de Castilla y León, Spain, and the European Union. Stay of J.F.J.-B. in Salamanca, Spain, was supported by fellowships from CONACYT, Mexico, and ALFA Program Micologia No.5.0118.9 from the European Union. J.F.J.-B. is a predoctoral fellow from CONACYT at Centro de Investigación y de Estudios Avanzados del IPN (Unidad Irapuato).

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