Small molecule inhibitors of protein translation are useful probes for identifying changes in ribosome function. This study utilized three such molecules: paromomycin, anisomycin and sparsomycin. The effects of all three drugs were monitored using dilution spot assays at 30 C on SD-trp media containing various drug concentrations. Paromomycin is an aminoglycoside antibiotic that increases translational error rates by artificially stabilizing codon:anticodon interactions at the decoding center in the small ribosomal subunit (31) . As compared to their intrinsic growth in the absence of drug, both the 51-4A and 54-7A mutants were slightly hypersensitive to 2 mg/ml paromomycin, as were Y52Á, Y52N and Y52H. In contrast, R51A, F57A and R61A were all paromomycin resistant ( Figure 2B ). Anisomycin competes with the 3 0 end of the aa-tRNA for binding to the A-site pocket of the ribosome (32, 33) . Both 51-4A and 54-7A showed anisomycin resistance at 40 mg/ml, as did several Y52* mutants, and R61A ( Figure 2B ). Sparsomycin binds to the P-site and interferes with peptidyl-tRNA binding and peptidyl transfer (33, 34) . 51-4A and 54-7A mutants were hypersensitive to 30 mg/ml sparsomycin, as were most of the Y52* mutants, with the exception of Y52F, which conferred slight resistance to this drug ( Figure 2B ).