Respiratory Chain Complex I Is Essential for Sexual Development in Neurospora and Binding of Iron Sulfur Clusters Are Required for Enzyme Assembly

Respiratory Chain Complex I Is Essential for Sexual Development in Neurospora and Binding of Iron Sulfur Clusters Are Required for Enzyme Assembly

Margarida Duarte^a and Arnaldo Videira^a,b
^a Instituto de Biologia Molecular e Celular, University of Porto, 4150-180 Porto, Portugal
^b Instituto de Ciências Biomédicas de Abel Salazar, University of Porto, 4150-180 Porto, Portugal

Corresponding author: Arnaldo Videira, Instituto de Biologia Molecular e Celular, Rua do Campo Alegre 823, 4150-180 Porto, Portugal., asvideir{at}icbas.up.pt (E-mail)

Communicating editor: J. J. LOROS

We have cloned and disrupted in vivo, by repeat-induced pointmutations, the nuclear gene coding for an iron sulfur subunitof complex I from Neurospora crassa, homologue of the mammalianTYKY protein. Analysis of the obtained mutant nuo21.3c revealedthat complex I fails to assemble. The peripheral arm of theenzyme is disrupted while its membrane arm accumulates. Furthermore,mutated 21.3c-kD proteins, in which selected cysteine residueswere substituted with alanines or serines, were expressed inmutant nuo21.3c. The phenotypes of these strains regarding theformation of complex I are similar to that of the original mutant,indicating that binding of iron sulfur centers to protein subunitsis a prerequisite for complex I assembly. Homozygous crossesof nuo21.3c strain, and of other complex I mutants, are unableto complete sexual development. The crosses are blocked at anearly developmental stage, before fusion of the nuclei of oppositemating types. This phenotype can be rescued only by transformationwith the intact gene. Our results suggest that this might bedue to the compromised capacity of complex I-defective strainsin energy production.

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