Worm Breeder's Gazette 11(4): 46
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.
N2 carries a tandem duplication of much of the unc-30 gene; the duplication is absent in B0. Sequencing of subclones of the N2 genomic lambda clone CB#RH17 reveals a first copy 5,592 bp in length, followed directly by 3,387 bp of a perfectly repeated second copy. ( This is potentially dangerous, as there is the slight possibility of gene conversion in the lambda clone.) At this position (a Sau3A site), CB#RH17 ends and another genomic lambda clone, CB#RH24, begins (see figure). Partial sequencing of subclones of CB#RH24 indicates that the second copy continues, probably to completion. (Sequence obtained so far includes a fragment which presumably represents the end of the second copy; it matches the end of the first copy and then diverges.) Much and perhaps all of the coding potential of the gene is duplicated. CB#RH12 and CB#RH17, both of which complement unc-30(e191) in transformation rescue experiments, end at Sau3A sites at equivalent positions in the first and second copies, respectively. I have previously reported that CB#RH12 breaks within an intron near the 3' end of the gene, and thus apparently directs synthesis of an altered but still functional product. In CB#RH17, the second copy might also direct synthesis of such a product, unless required 5' sequences are missing. (The ends of the unc-30 transcript have not been defined.) Since CB#RH12 contains none of the second copy, it seems probable that the first copy represents the real unc-30 gene, but this is not formally proven. Further comment awaits completion of the sequence of the second copy, which may reveal differences and an assay which distinguishes the two copies. This may all be irrelevant to the prediction of the amino acid sequence of the putative unc-30 protein. By genetic criteria, only one of the two copies of unc-30 seems to function. The six ems-induced alleles reported by Brenner ('74) appeared to arise at about knock-out frequency. The eleven mutant alleles of unc-30 of which I am aware are all simple recessives. I have constructed all the heteroallelic combinations of ten alleles, and no pair complements. (nT1 [unc-30(e2327)] wasn't tested. Two alleles, e2384 and bx7, were induced on B0 chromosomes, which contain only one copy of the gene.) The first 3.4 kb of the duplication, and probably more, are perfectly repeated, indicating that it arose recently in C. elegans evolution. I have examined a set of wild strains by Southern blotting. The Anglo-American strains N2 (Bristol), DH424 (California) and TR403 (Wisconsin) carry the duplication; the Continental strains B0 ( Bergerac) and RC301 (Freibourg) carry a single copy. (Does anyone have a strain from Martinique, or Louisiana! ?) Given the duplication, one might expect that certain unc-30 mutations would revert by gene conversion. A strain carrying the allele e596 appears to have reverted during passaging, but since I have no molecular assay for the allele, I cannot exclude the possibility of contamination by an N2 animal. The 'revertant' is fully wild-type, retains the duplication, and is tightly linked to unc- 30. Incidentally, e596 is incompletely, but significantly suppressed by smg-1(e1228).The position of the unc-30 transcript in the figure is based on analysis of the sequences of CB#RH17 and two cDNA clones. The predicted stop codon is 503 bp upstream of the beginning of the second repeat. [See Figure 1]