Worm Breeder's Gazette 10(1): 95
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.
The ama-1 IV gene encodes the largest subunit of RNA polymerase II, and is defined by dominant, amanitin-resistance mutations (Sanford, Golomb and Riddle, J. Biol. Chem. 258:12804-12809, 1983) as well as recessive-lethal mutations (Rogalski and Riddle, Genetics, in press). The region of chromosome IV surrounding ama-1 has been genetically characterized, and deficiencies and duplications that include this gene have been identified. We have determined that the null phenotype of ama-1 is developmental arrest after hatching from the egg. Thus, there is sufficient maternal RNA polymerase II in C. elegans to complete embryonic development, and de novo RNA polymerase II synthesis is not required until the L1 stage. Nine of the 21 lethal ama-1 alleles obtained thus far exhibit the null phenotype at both 20 C and 25 C. One unique allele exhibits an embryonic-arrest phenotype at 20 C, but an L1-lethal phenotype at 25 C. This mutant may encode a product that interferes with the wildtype maternal RNA polymerase II during embryogenesis. The mutant function appears to be thermolabile, since the null phenotype is observed at 25 C. The eleven remaining ama-1 alleles result in partial loss of RNA polymerase II function. One of these results in developmental arrest during the L2 stage, whereas the others affect fertility in adult hermaphrodites and/or embryonic development in their progeny. All but one of the ama-1 hypomorphs exhibit a more severe phenotype at 25 C than they do at 20 C. Sixteen of the 21 lethal alleles have been positioned in the ama-1 fine-structure map (see Bullerjahn and Riddle, this issue). Reversion experiments were performed with 17 of the ama-1 lethal alleles described above to identify intragenic revertants and unlinked suppressors of these mutations. Revertants were detected as rare amanitin-resistant progeny of mutagenized dpy-13(e184) 8mx) / nT1[ama-1(+) (IV); +/nT1(V) hermaphrodites, where mx represents the lethal mutation. Normally hermaphrodites of the above genotype do not produce amanitin-resistant progeny, since they carry one nonfunctional ama-1 allele and one amanitin-sensitive allele. However, a mutation that restored the dominant, amanitin- resistance phenotype of ama-1(m118) would result in a resistant individual. Also, resistant animals would be obtained if a new amanitin-resistance ama-1 mutation were induced on the nT1(IV) chromosome. The nT1 translocation was used in these experiments to prevent intragenic recombination between the lethal and m118 mutations. Fifteen amanitin-resistant revertants were obtained in these experiments after screening a total of 2.5x10+E7 animals. Eight carried new amanitin-resistance mutations linked to the nT1 translocation, whereas the other seven were apparent intragenic revertants. Five of the intragenic revertants were isolated in the m118m236 allele, which exhibits a sterile phenotype at 20 C. The m118m367 and m118m370 null mutations were the other two alleles that reverted. Not all of the ama-1 revertants are wild-type in phenotype, suggesting that RNA polymerase II function may not be completely restored. Some of these strains should provide altered enzymes suitable for biochemical analysis.