Cloning and characterization of a cDNA coding for Candida albicans polyubiquitin

Immunoscreening of a Candida albicans cDNA library in the expression vector lambda gt11 with rabbit polyclonal antibodies against the 37 kDa cell surface laminin receptor of C albicans resulted in the isolation of a cDNA clone of 0.9 kb. Sequencing of this clone demonstrated a full length open reading frame encoding the polyubiquitin, which contains three tandem copies, head-to-tail spacerless repeats, of the 228 nucleotides coding for the 76 amino acids of the ubiquitin protein, which is identical to that of Saccharomyces cerevisiae. The third copy possesses an extra C-terminal amino acid which is distinct to that found in S. cerevisiae. Northern blot analysis revealed a single mRNA population of about 1 kb present in similar amounts in both yeast and mycelial cells. This indicates that the C. albicans polyubiquitin gene (UBI1) encodes a polyubiquitin precursor protein containing three ubiquitin repeats. Immunofluorescence and Western immunoblotting experiments with polyclonal antibodies against mammalian ubiquitin suggest the presence of ubiquitinated protein moieties in the wall of C. albicans cells.