Evolutionary divergence of an elongation factor 3 from Cryptococcus neoformans

Elongation factor 3 (EF3) is considered a promising drug target for the con trol of fungal diseases because of its requirement for protein synthesis an d survival of fungi and a lack of EF3 in the mammalian host. However, EF3 h as been characterized only in ascomycete yeast. In order to understand the role of EF3 in a basidiomycete yeast, we cloned the gene encoding EF3 from Cryptococcus neoformans (CnEF3), an important fungal pathogen in immunocomp romised patients, including those infected with human immunodeficiency viru s. CnEF3 was found to encode a 1,055-amino-acid protein and has 44% identit y with EP3 from Saccharomyces cerevisiae (YEF3). Expressed CnEF3 exhibited ATPase activity that,vas only modestly stimulated by ribosomes from S. cere visiae. In contrast, CnEF3 showed tight binding to cryptococcal ribosomes, as shown by an inability to be removed under conditions which successfully remove Saccharomyces EF3 from ribosomes (0.5 M KCl or 2 M LiCl). CnEF3 also poorly complemented a YEF3 defect in a diploid null mutant and two tempera ture-sensitive mutants which have been shown previously to be complemented well by EF3 from other ascomycetes, such as Candida albicans. These data cl early identify the presence of a functioning EF3 in the basidiomycete yeast C. neoformans, which demonstrates an evolutionary divergence from EF3 of a scomycete yeast.