J. Biol. Chem., Vol. 261, Issue 15, 6919-6923, May, 1986
The selective release of one of the two L7/L12 dimers from the Escherichia coli ribosome induced by a monoclonal antibody to the NH2- terminal region
DS Tewari, A Sommer and RR Traut
Two monoclonal antibodies against different epitopes in Escherichia coli
ribosomal protein L7/L12 were prepared and characterized as reported
previously (Sommer, A., Etchison, J.R., Gavino, G., Zecherle, N., Casiano,
C., and Traud, R.R. (1985) J. Biol. Chem. 260, 6522-6527). Both antibodies
strongly inhibited polyuridylic acid-directed polyphenylalanine synthesis,
ribosome-dependent GTPase activity, and the binding of elongation factor G
to the ribosome at mole ratios over ribosomes of 4:1 or less. One epitope
was shown to be within residues 1- 73 (Ab 1-73) and the other within 74-120
(Ab 74-120). Incubation of 50 S ribosomal subunits or 70 S ribosomes with
Ab 1-73, but not with Ab 74- 120, leads to a partial loss of L7/L12 from
the particle with no loss of any other protein. The experiment was repeated
with ribosomes reconstituted with pure radioactive L7/L12 of determined
specific activity in order to quantify the L7/L12 in the antibody-treated
particle. The protein-deficient core particles isolated by sucrose gradient
centrifugation after incubation with Ab 1-73 were found to contain, on
average, two copies of L7/L12 and one Ab 1-73. The constancy of this
stoichiometry in many experiments and the demonstration of Ab 1-73 on all
particles indicate the presence of a homogeneous population of ribosomes,
each with only one of the two L7/L12 dimers originally present. The results
show a difference in the interactions of the two dimers with the ribosome
and present a means of preparing ribosomes with one dimer in a specific
binding site. The accompanying paper (Olson, H.M., Sommer, A., Tewari, D.
S., Traut, R.R., and Glitz, D.G. (1986) J. Biol. Chem. 261, 6924-6932)
shows by immune electron microscopy the location of the two
antibody-binding sites and the effect of Ab 1-73 on structure.