Absence of genes homologous to Saccharomyces cerevisiae MDL1, YEF3 and YDR061W is particularly remarkable as those groups are nearly ubiquitously present in the genomes of asco- and basidiomycetes analysed so far [14, 15], and YEF3 (encoding the translation elongation factor 3) has shown to be essential for vegetative growth in S. cerevisiae [19].