Worm Breeder's Gazette 11(1): 40
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.
To understand the molecular mechanism of thick filament assembly, we are investigating the mutation site of EMS induced unc-15 mutants at the DNA level. These mutant alleles are distinguished two categories. One is e1214, has no detectable paramyosin on SDS-PAGE gels and apparently null phenotype. This mutant had amber nonsense mutation (Q to Amber) near the N-terminus. The others are missense alleles which accumulate normal level's paramyosin, nevertheless result in the disruption of thick filament assembly. The latter alleles are of variable phenotype, the most severely paralyzed allele, e73 caused the reversion of electric charge (E- to K+) by the point mutation. Further sequence analysis of two intragenic e73 revertants revealed that second mutations are exactly in the unc-15 gene, not in a closely linked gene, and also caused the reversion of electric charge (E- to K+). These mutation might not disrupt the secondary structure of paramyosin, but only change the charge on the surface of alpha-helical coiled coil structure. This might mean the assembly of paramyosin itself and/or paramyosin-myosin heavy chain result from charge interactions between the molecules. We hope to calculate what kind of changes are induced by each of substituted amino acid with the computer program exploited by Dr. McLachlan (McLachlan, A. D. and Karn, J,1982, Nature 299, 226-231; McLachlan, A. D. and Karn, J, 1983, J. Mol. Biol. 164, 605-626; Kagawa, H., Gengyo, K., McLachlan, A. D., Brenner, S. and Karn, J., 1989, J. Mol. Biol., 207, 311-333). Molecular organization of unc-15 alleles summarized. More detailed epitope mapping of paramyosin is in progress. [See Figure 1]