, 2007). Selfing occurs under conditions favourable for sexual development, with closed fruiting bodies (cleistothecia), containing ascospores, being formed by all fertile strains (see Todd et al., 2007). Previously, we found that pex mutants, impaired in PTS1 protein import, were affected in sexual development, producing low numbers of small cleistothecia in selfings or homozygous crosses (Hynes et al., 2008). However, it was clear that meiosis was not blocked. We have find more now deleted the gene encoding Pex2 in order to test whether meiotic commitment is dependent on the RING-finger complex in A. nidulans. Unlike P. anserina, meiosis is not

affected, indicating a fundamental difference between these species. The media and conditions for growth of A. nidulans and standard genetic manipulations were as described previously (Todd et al., 2007). DNA from transformants was analysed by Southern blotting to confirm predicted integration events. Standard methods for DNA manipulations, nucleic acid Compound Library blotting and hybridization have been described (Hynes et al., 2006). Unless otherwise indicated, strains contained the veA1 mutation.

This mutation results in increased conidiation and reduced sexual reproduction relative to veA+ strains (Kim et al., 2002). The isolation of the pexC∷bar and pexC∷bar; ve+ strains has been described (Hynes et al., 2008). A single gene encoding the homologue of Pex2 was identified as AN4056.3 in the A. nidulans genome database (http://www.broadinstitute.org/annotation/genome/aspergillus_group/MultiHome.html). A 2.7-kb fragment corresponding to coordinates −598 to +2098 (relative

to the predicted translation start) was amplified by the PCR using the primers 5′-AACATCCCCGCAAGATACAG-3′ and 5′-ATGAGTTCGAGAAGCGTCGT-3′ and inserted into EcoRV cut pBluescript SK+ to generate the plasmid pFK7442. A 2.1-kb XhoI–E coICRI fragment containing the Aspergillus fumigatus riboB gene (Nayak et al., 2006) was inserted between the XhoI and StuI sites of the insert of pFK7442 to generate pFK7447, thereby replacing sequences of AN4056 (+209 to +1177) corresponding to amino acids 71–379 (Fig. 1a). A SSR128129E linear PCR fragment generated with the above primers was used to transform strain TNO2A21 (genotype pyroA4 nkuAΔ; veA1 riboB2) selecting for riboflavin prototrophy using standard methods (Nayak et al., 2006). The recipient strain contained the nkuAΔ to promote homologous integration events. blastp searches of the predicted proteins from the A. nidulans genome sequence with the P. anserina Pex2 sequence revealed a single homologue (AN4056.3) in agreement with the analysis of Kiel et al. (2006). The A. nidulans gene contains only one intron, while the predicted pex2 genes of other Aspergillus spp. contain two introns (Kiel et al., 2006). AN4056 was designated pexB in accordance with the standard nomenclature for A. nidulans.