Worm Breeder's Gazette 7(1): 58
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.
We thought that unc-92, a dominant unc with disorganized muscle and a high reversion frequency, might be an actin gene because of its phenotype and because of its map position (Newsletter 6, 23 (1981)). Using a Bergerac strain/Bristol strain DNA polymorphism adjacent to the cluster of actin genes I, II and III, we were able to locate the actin cluster between unc-23 and sma-1. The arrangement of actin genes I, II and III within a 12 kb stretch of DNA suggested mechanisms for the high unc-92 reversion frequency, including gene conversion between genes and nonhomologous recombination. Nonhomologous recombination should reduce three genes to two which would be easy to detect by Southern blot analysis. We therefore obtained from Bob Waterston six revertants of the St15 allele of unc-92; three revertants arose spontaneously and three were obtained after an EMS mutagenesis. We isolated DNA from each revertant strain and analyzed it by Southern blot analysis. Five of the revertants showed a pattern identical to that of both St15 and N2 when probed for actin sequences, but one revertant, RW2246, which derived from the EMS mutagenesis, showed an anomalous pattern. Further restriction mapping of RW2246 by Southern blot analysis revealed that this revertant contained a 5kb deletion that fused the 5' portion of gene II to the 3' portion of gene III. The fusion could have been the result of recombination between genes II and III, deleting the unc-92 lesion and creating a new hybrid gene. We believe that the revertant phenotype resulted from this fusion. Because most of the differences between actin genes occur at their 5' ends, the fusion leaves the revertant with the equivalent of only genes I and II. Despite the lack of gene III, the revertant appears wild type because genes I and III appear thus far to be identical by restriction endonuclease and sequence analyses. We therefore believe that unc-92 is the actin gene cluster, although final proof awaits comparison of the actin DNA sequences of N2 and St15.