A novel form of ubiquitin found in the basidiomycete fungus, Coprinus congregatus.

Ubiquitin is considered one of the most highly conserved eukaryotic proteins. A remarkable 72 out of 76 amino acid residues are invariant in the ubiquitins of fungi, plants and vertebrates. To date, the ubiquitin sequences of only two fungi have been reported, those of Sacchoromyces cerevisiae (1) and Neurospora crassa (2). These fungi are both ascomycetes, and not surprisingly their ubiquitin protein sequences are identical. We present here the nucleotide sequence and deduced amino acid sequence of one of at least five ubiquitin coding repeats found in the basidiomycete fungus, Coprinus congregatus. A combination of PCR and conventional cloning techniques was used to identify and clone Coprinus congregatus genomic and cDNA sequences coding for ubiquitin. The deduced amino acid sequence indicates that Coprinus congregatus ubiquitin constitutes a new variant of ubiquitin protein. This new form of ubiquitin differs from that found in the ascomycete fungi only at amino acid number 28, where an alanine has been substituted for the serine found in the ascomycete species. Interestingly, the alanine at position number 28 is conserved in humans, plants, and two of the four newly reported divergent Tetrahymena sequences (3). ACKNOWLEDGEMENT