Coordinate Inhibition of Elongation Factor G Function and Ribosomal Subunit Association by Antibodies to Several Ribosomal Proteins*

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We previously showed that treatment of Escherichia coli ribosomes with antibodies specific for proteins L7 and L12 inhibits both EF-G·GDP binding and ribosome-dependent GTP hydrolysis (Highland et al. (1973) Proc. Nat. Acad. Sci. USA 70, 142-150; and Kischa et al. (1971) Nature New Biol. 233, 62-63). We now report that antibodies to six additional proteins also inhibit GTP hydrolysis, but do not inhibit EF-G·GDP binding. Moreover, inhibition by these antibodies is dependent on the state of association of the treated ribosomes. When 70S couples are treated, only antibodies to proteins L14 and L23 are inhibitory and then only partially. However, when separated ribosomal subunits are treated individually and then mixed with the complementary untreated subunits, inhibition by antibodies L14 and L23 is complete, and antibodies to proteins L19, L27, S9, and S11 now show an inhibitory effect. In addition, treatment of subunits with any of these six antibodies (but not those to L7 or L12) results in inhibition of reassociation, which is presumably responsible for the inhibition of hydrolysis. These data suggest that the area of interaction between EF-G and the ribosome is restricted to proteins L7 and L12, and that antibodies to proteins L14, L19, L23, L27, S9, and S11, but not L7 and L12, block the physical association of the subunits.

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