Nucleic Acids Research, 1982, Vol. 10, No. 18 5681-5693
© 1982
MOLECULAR BIOLOGY |
Chain initiation factor 3 crosslinks to E. coli 30S and 5OS ribosomal subunits and alters the UV absorbance spectrum of 70S ribosomes
Department of Biochemistry, The University of Mississippi Medical Center 2500 North State Street, Jackson, MS 39216, USA
Received May 10, 1982. Revised August 20, 1982. Accepted August 20, 1982.
We report a direct procedure to determine the proteins near the IF-3 binding site in purified 30S and 50S ribosomal subunits. This procedure introduces only limited numbers of cleavable crosslinks between IF-3 and its nearest neighbors. The cleavable crosslinking reagent, 2-iminothiolane, was used to crosslink IF-3 in place to both 30S and 50S subunits. Ribosomal proteins S9/S11, S12, L2, L5 and L17 were found, by this approach, to be In close proximity to the factor in purified IF-3-subunit complexes.
In addition, IF-3 was shown to alter the ultraviolet absorbance spectrum of E. coll 70S ribosomes at 10 mM Mg2+. The magnitude of the observed difference spectrum at a constant IF-3/ribosome ratio of 1.0, is linearly dependent upon rlbosome concentration over the range 5 nM - 55 nM. Titration experiments indicated that the observed effect is maximal at an IF-3/ribosome ratio of approximately 1.0. These results are taken to indicate a conformational change in the 70S ribosome induced by IF-3.