Worm Breeder's Gazette 5(2): 26
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.
Using a combination of genetic and physical techniques, twenty independent deletions that affect the unc-54 myosin heavy chain gene have been identified. Eighteen of these deletions were isolated using a selective technique previously described (1979 C. elegans meeting abstracts). Briefly, this selection is based upon relief from the dominant effects of the unc-54 mutation e1152. New recessive mutations are selected because they eliminate the dominance of e1152 and yield phenotypically wild-type heterozygotes. A large collection of EMS and DE0 (1,2,7,8-diepoxyoctane) induced unc-54 mutations has been analyzed for the presence of deletions. Thirteen deletions have been identified by genetic criteria. Each is lethal when homozygous. Each maps as a deletion of chromosome 1 material that includes unc-54. In order to demonstrate this, a number of essential genes near unc-54 has been defined by the isolation of point mutations that are recessive to wild-type and lethal when homozygous. Complementation tests between unc-54 deletion mutations, the nearby recessive lethal point mutations, and other mutations previously shown to be near unc-54 allow a detailed fine structure map of the chromosomal region surrounding unc-54 to be constructed. This map is shown below. An additional seven deletion mutations have been identified by physical criteria. Each is viable when homozygous but exhibits an altered pattern of DNA restriction fragments from the unc-54 region. In each case, the altered pattern indicates that the mutation results from simple deletion of DNA sequences. Six of these deletions are small (~100-600 base pairs) and one is greater than 15 kilobase pairs in length. Each affects unc-54 mRNA coding sequences. The precise location of all deletion alleles upon the physical map of this chromosomal region is currently being determined. The number and sizes of deletions among total alleles are strikingly different for EMS and DE0 induced mutations. For DE0, approximately 17% (13/77) of total alleles are deletions by genetic criteria, and therefore very large. Another 6% (3/50) are deletions by only physical criteria, and are quite small. Thus, approximately 23% of DE0 induced mutations are deletions. For EMS, less than 3% (0/36) of total alleles are deletions by genetic analysis. However, 16% (4/25) are deletions of small regions of the gene (200-600 base pairs). Clearly, these sample sizes are not large enough to make strong statements, but something looks odd. [See Figure 1]