Worm Breeder's Gazette 11(2): 48
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.
Sequencing of a 13.5kb genomic fragment sufficient for transformation rescue of unc-31 is almost complete, but has not yet revealed anything new about the function of the unc-31 gene product. The sequence contains a pair of imperfect direct repeats about 200bp in length. One copy of the repeat is within an intron of the unc-31 gene, and the other is beyond the 3' end of unc-31 (Fig. a). Sequences within the repeats are homologous to U5 snRNA genes; they are apparently U5 snRNA genes or pseudogenes. The sequences of the putative genes differ at several positions from that of the previously described C. elegans U5-1 gene (Thomas et al. WBG 11:1), but can be folded into the same secondary structure (Fig. c). The new genes have been named U5-2 and U5-3, and the locus has been named rsn-13. Both new genes have the conserved upstream sequence (proximal sequence element or PSE) found about 50bp upstream of other nematode snRNA genes (Thomas et al. CSH abst's '89). The PSE of the U5-2 gene has one mismatch from the consensus in a highly conserved base (Fig. b, position -47). The predicted RNA products of U5-2 and U5-3 are identical except for one base change in the 3' hairpin loop (Fig.b, position +111; Fig. c). Differences between U5-3 and U5-1 are circled (Fig. c). Note the compensatory changes in the stem of the 3' hairpin. Recombination between the repeat sequences would result in a 5.2kb deletion removing much of the unc-31 gene. The [32P]-induced unc-31 allele e928 contains a 5.2kb deletion in this region. It is tempting to suppose that such a recombination event led to the observed deletion. The TR679-induced allele u378 also contains a 5.2kb deletion, but the deletion breakpoints have not been as well mapped. Progress is being made in the characterization of the unc-31 gene itself. -galactosidase translational fusion constructs made from the 5' end of the unc-31 gene and Andy Fire's vectors. Initial results from transformed lines containing extrachromosomal arrays suggest that the gene is expressed in a small number of neurones in the lateral and ventral ganglia. Evaluation of these results and identification of the cells is in progress. Figures: a) Open box spans the e928 deletion. Direction of transcription of genes indicated by arrows. The 13.5kb fragment extending from the left end of CB#RH1A to the XhoI site complements unc-31(e928). b) Asterisks indicate matches between the two repeats. Mismatches with the C. elegans PSE consensus are underlined. c) U5-3 RNA secondary structure after the model proposed by Thomas et al.. Differences between U5-3 and U5-1 are circled. An arrow points to the single difference between U5-3 and U5-2. [See Figures 1-2]
