Worm Breeder's Gazette 12(5): 79 (February 1, 1993)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Higher organisms produce ubiquitin from three types of gene loci. We have isolated two of these types from C. elegans (UbiA-Mol. Cell. Biol. (1989)9: 268-271) and UbiB(WBG 12(3) 63)). The third type, which encodes a fusion of ubiquitin with an 80 amino acid ribosomal protein, had eluded us. We were recently able to locate this transcript by PCR using an oligonucleotide primer which bound to the SLl trans-splice leader sequence and a degenerate oligonucleotide primer matching the published sequence of the ribosomal protein. Surprisingly, this fragment had a ubiquitin-like sequence rather than ubiquitin fused to the ribosomal protein sequence. The ubiquitin-like sequence shares 38% amino acid sequence identity with C. elegans ubiquitin. This appears to be a (so far) unique form of this fusion transcript in higher organisms. Genomic and additional PCR data confirmed that the ribosomal protein is not made fused to bona fide ubiquitin in C. elegans. As such, this gene product will provide some interesting insights into ubiquitin expression and processing.
We have found that C. briggsae also has the ubiquitin-like fusion, but we don't yet know if other nematodes share this divergent form of the transcript. If so, it could provide data on the relatedness of nematode species, genera, or higher orders.
We have also looked for introns in the ubiquitin-like portion of the gene to see if their positions correspond to the positions of introns in the other two C. elegans ubiquitin genes. The C. elegans and C. briggsae ubiquitin-like fusion genes both have a single intron which interrupts a glycine codon. Alignment of the ubiquitin-like sequence with C elegans ubiquitin genes shows that this is the same glycine codon at which introns occur in both UbiA and UbiB. This suggests that the ubiquitin-like sequence is structurally derived from ubiquitin ( or vice versa).
Supported by the Medical Research Council of Canada.