Worm Breeder's Gazette 12(3): 39 (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.
A database search against spe-26 (a gene involved in the early stages of C. elegans spermatogenesis) revealed a highly conserved intron motif shared by a number of other C elegans genes. This motif, about 100 bp long, is found in the fourth and largest (294 bp) spe-26 intron, and in confirmed or postulated introns at least once in six other sequences. The other sequences are: myoD, ben-l, unc-93 and cosmids ZK637 , ZK643 (two regions), and F59B2 .The spe-26 and unc-93 sequences (and to a lesser degree, the myoD sequence) contain an imperfect inverted repeat of about 200 bp, each half of which contains the motif. Searches have not found this motif in any other species, but it has turned up many times among the relatively small C. elegans database, so we suspect this sequence may have biological relevance in worms.
Further experiments provide circumstantial evidence supporting this notion. The upstream region of spe-26 does not contain the canonical sequence elements typically associated with promoters. We have tested 5' deletions of spe-26 for their ability to rescue the Spe-26 defect. Although fertility (i.e.. brood size) decreases as more upstream DNA is deleted, there is some degree of rescue even after deleting to 15 bp from the start codon. 3' deletions to within about 50 bp of the polyA addition site gave similar results. However, a construct that had complete 5' and 3' genomic regions precisely fused to a cDNA clone (i.e.. the same as the genomic clone but lacking introns) fails to rescue. When the entire 5' genomic region was tested for promoter activity by lacZ reporter fusion injections, we saw no sperm-specific and little ectopic ß-galactosidase expression. These results suggest that the flanking sequences contribute little to spe-26 expression, whereas something in the introns seems to be essential. We are currently constructing and testing plasmids containing different combinations of the five spe-26 introns to determine which is (are) necessary for expression. Our hope is that intron 4 contains a regulatory element and that a new and widespread mode of C. elegans gene expression will be revealed [See Figure 1].
*Since this letter was first drafted we have tested a spe-26 construct deleted only in introns 4 and 5--IT RESCUED, but gave about half the fertility of the intact construct. The story is clearly not complete.