Worm Breeder's Gazette 9(3): 44

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Fine Structure Map of an Essential Gene, ama-1

A.M.E. Bullerjahn and D.L. Riddle

Figure 1

The ama-1 gene, which is located 0.05 map units to the right of dpy-
13 on LG IV, encodes the amanitin-binding subunit of RNA polymerase II.
The gene was originally defined by the dominant mutation, m118, which 
conveys resistance to  -amanitin (Sanford, Golomb, and Riddle, 1983, J.
Biol. Chem. 258, 12804-12809). Twenty amanitin-sensitive mutants that 
carry recessive-lethal alleles of ama-1 were isolated following EMS 
mutagenesis of resistant parents (Rogalski et al. WBG: Vol. 8, No. 3, 
and Vol. 9, No.l). 
We are working on a fine-structure analysis of ama-1 and have mapped 
14 of these lethal mutations in five-factor crosses with respect to 
m118, dpy-13, e of genotype f dpy-
13(e184) 8 mX) +/unc-17(e245) + + unc-S(e53) are 
put into I ml liquid cultures with 3% OP50 and 20  g/ml  -amanitin. 
Only worms in which recombination between the resistance mutation (
m118) and the lethal mutation (mX) has occurred will grow in the 
amanitin. If the lethal mutation is to the right of the resistance 
mutation, then the resistance-bearing chromosome is + dpy-13(e184) 
8) ), and recombinants carrying 
this chromosome will be either Dpy or Unc-5. If the lethal mutation is 
to the left of m118, then the recombinant chromosome is unc-17(e245) + 
ama-1(m118) +, and animals carrying this chromosome will be either Unc-
17 or semi-Dumpy. There is an average of 500,000 worms in each 
A different strategy is being employed to order lethal mutations 
with respect to each other. This requires the construction of 
heteroallelic lethal strains, so mDp1 red for 
viability (see Rogalski et al., this issue). For example, amanitin-
resistant progeny are to be selected among progeny of mDp1 
45) 45) 
84) 8 m328) +/ + dpy-13(e184) 
8 m329) unc-S(e53) heterozygotes. 
The figure shows the ama-1 fine-structure map. Allele names are 
given along with phenotypes exhibited at 20 C (em1=embryonic lethal, 
ell=early larval lethal, m11=mid-larval lethal, sa=sterile adult). The 
map is 0.018 map units long, and the m118 mutation is near the dpy-13 
end. The lethals have not yet been ordered with respect to each other, 
so positions are based on recombination frequencies with m118. We are 
unable to separate 4 of the adult sterile mutations from m118. So far, 
all of the early larval lethal mutations map to the right of the m118 
mutation, and only the mid-larval and embryonic lethal mutations map 
to the left of m118. This represents the first fine-structure map of 
an essential gene in C. ope that this will be 
useful to guide the DNA sequence analysis of selected mutant ama-1 

Figure 1