Pactamycin

Abstract: We have studied the interactions of the antibiotics apramycin, kasugamycin, myomycin, neamine and pactamycin with 16S rRNA by chemical probing of drug-ribosome complexes. Kasugamycin and pactamycin, which are believed to affect translational initiation, protect bases in common with P-site-bound tRNA. While kasugamycin protects A794 and G926, and causes enhanced reactivity of C795, pactamycin protects G693 and C795. All four of these bases were previously shown to be protected by P-site tRNA or by edeine, another P-site inhibitor. Apramycin and neamine, which both induce miscoding and inhibit translocation, protect A1408, G1419 and G1494, as was also found earlier for neomycin, gentamicin, kanamycin and paromomycin. A1408 and G1494 were previously shown to be protected by A-site tRNA. Surprisingly, myomycin fails to give strong protection of any bases in 16S rRNA, in spite of having an apparently identical target site and mode of action to streptomycin, which protects several bases in the 915 region. Instead, myomycin gives only weak protection of A1408. These results suggest that the binding site(s) of streptomycin and myomycin have yet to be identified.

Abstract: We have studied the effect of the drug pactamycin on protein synthesis in poliovirus-infected HeLa cells. At a concentration which primarily inhibits initiation of protein synthesis, the spectrum of poliovirus proteins synthesized is markedly changed. The amount of NCVP 1, the capsid precursor, is greatly reduced relative to NCVP 2 and the amount of NCVP X is slightly reduced. Since it is believed that there is only one major site for the initiation of protein synthesis on the poliovirus genome, we interpret this differential effect on the poliovirus proteins to be an indication of their relative distance from the initiation site. On this basis, we propose a gene order for the poliovirus genome (5' -> 3') of NCVP 1, NCVP X, NCVP 2.