Biochemical analysis of the role of cytoplasmic ribosomes of Coprinus cinereus in cycloheximide resistance.

The development of an optimized in vitro polyuridylic acid-dependent polyphenylalanine-synthesizing system using cell-free extracts of the basidiomycete fungus Coprinus cinereus is described. The in vitro assay has been used to show that cycloheximide-resistant strains CY8.2, CY9.23 and Sp98, all mutant at the cy-2 locus, have cytoplasmic ribosomes which are more resistant to the drug than the corresponding sensitive strains, CY8, CY9 and CY3. Cycloheximide concentrations and molar ratios of cycloheximide to ribosomes required for 50% inhibition in vitro under standard assay conditions are presented for these strains. The molar ratio required for 50% inhibition in vitro is dependent on the concentration of ribosomes in the assay.