Suppression of methionine mutants in Coprinus

Summary The met-1-1 mutation in Coprinus lagopus is known to be suppressed by five recessive non-allelic suppressor genes (sup-1 to sup-5). Two of these genes complement normally in heterozygotes but the other three fail to complement each other in any combination. Four of the suppressor genes, sup-1, sup-2, sup-3 and sup-5, were tested for ability to suppress met-1-2 a second met-1 mutation. Non-identity of the two met-1 alleles was first confirmed by demonstrating intragenic recombination. The complementing suppressors, sup-1 and sup-2, proved to be allele unspecific and suppressed both met-1 mutations. The non-complementing suppressors, sup-3 and sup-5, were allele specific and could only suppress the met-1-1 mutation. This is interpreted to mean that sup-1 and sup-2 act indirectly to circumvent the metabolic lesion caused by any met-1 mutation whereas sup-3 and sup-5 are missense informational suppressors involving modified tRNA species which specifically mistranslate the met-1-1 mutant codon.