UBA 1: an essential yeast gene encoding ubiquitin-activating enzyme.

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Abstract
All known functions of ubiquitin are mediated through its covalent attachment to other proteins. The post‐translational formation of ubiquitin–protein conjugates is preceded by an ATP‐requiring step in which the carboxyl terminus of ubiquitin is adenylated and subsequently joined, through a thiolester bond, to a cysteine residue in the ubiquitin‐activating enzyme, also known as E1. We report the isolation and functional analysis of the gene (UBA1) for the ubiquitin‐activating enzyme of the yeast Saccharomyces cerevisiae. UBA1 encodes a 114 kd protein whose amino acid sequence contains motifs characteristic of nucleotide‐binding sites. Expression of catalytically active UBA1 protein in E. coli, which lacks the ubiquitin system, confirmed that the yeast UBA1 gene encodes a ubiquitin‐activating enzyme. Deletion of the UBA1 gene is lethal, demonstrating that the formation of ubiquitin–protein conjugates is essential for cell viability.