Worm Breeder's Gazette 12(3): 63 (June 15, 1992)
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.
Eukaryotes in general have three types of ubiquitin genes: a polyubiquitin gene which encodes multiple tandem copies of ubiquitin transcribed as a polyprotein and two other genes which are fusions of ubiquitin with either a 52 aa or an 80aa ribosomal protein.
The polyubiquitin gene from C. elegans was described a few years ago by Roger Graham (Mol. Cell. Biol. (1989)2: 268-271). Since then, we have been studying the regulation of this gene and searching for additional ubiquitin genes. Roger was able to isolate a clone for the 52 aa fusion using a protocol he described in WBG (1990) 11(2):69. A subclone of the ribosomal-protein encoding region was used to probe a YAC grid. A single positive was found, on chromosome III.
The most notable aspect of the organization of this gene is the number and position of introns. Two introns occur in the ubiquitin portion of the gene. The position of the first is the same as that in four repeats of the polyubiquitin gene. (C. elegans is the only organism known to have introns in the polyubiquitin gene.) The second intron splits the two terminal glycine residues of ubiquitin. Neither of these intron positions coincides with those in any other 52 aa fusion gene [See Figure 1].
The sequence of a cDNA clone for this gene, isolated from Bob Barstead's lZAP library, shows that the message is trans-spliced. As an additional bonus, this gene has a recognizable TATA motif (unlike the poyubiquitin gene) which is 138 bp from the ATG start codon.
We have produced and are currently injecting constructs of this gene. We expect it to be universally constitutive (since it encodes a ribosomal protein) and hope that the promoter may have some practical use. In addition, we may even find out why these ribosomal proteins are always made fused to ubiquitin and what the fate of the ubiquitin part of the fusion is. The search for the third ubiquitin gene continues
Roger Graham. WBG (1990) 11(2):69