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Ubiquitin gene structure and expression in Caenorhabditis elegans Graham, Roger Walter


Ubiquitin is a multifunctional 76 amino acid protein which plays critical roles in many aspects of cellular metabolism. Ubiquitin protein structure and gene structure are highly conserved among eukaryotes. In C. elegans the major source of ubiquitin RNA was shown to be the polyubiquitin locus, UbiA. UbiA was shown to be transcribed as a polycistronic mRNA which contained eleven tandem repeats of ubiquitin sequence and possessed a two amino acid carboxy terminal extension on the final repeat. Mature UbiA mRNA was demonstrated to acquire a 22 nucleotide leader sequence via a trans splicing reaction involving a 100 nucleotide splice leader RNA derived from a different chromosome. UbiA was also shown to be unique among known polyubiquitin genes in containing four cis spliced introns within its coding sequence. Thus UbiA was shown to be one of a small class of genes found in higher eukaryotes whose hnRNA undergoes both cis and trans splicing. The expression of the UbiA gene was studied under various heat shock conditions, and was monitored during larval molting and throughout the major stages of development. These studies indicated that the expression of the UbiA gene was not inducible by acute or chronic heat shock, and did not appear to be under nutritional or developmental regulation. A second ubiquitin gene, UbiB, was cloned from C. elegans and a related nematode species C. briggsae. This gene was comprised of (at least) one ubiquitin unit followed by a basic 52 amino acid tail sequence.

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