JBC, Vol. 250, Issue 17, 6880-6884, Sep, 1975
Binding of Met-tRNAf to native 40 S ribosomal subunits in Ehrlich ascites tumor cells
K. E. Smith and E. C. Henshaw
Two forms of native 40 S ribosomal subunits, distinguishable by their
buoyant densities, are recovered from Ehrlich ascites cells. In this
communication, we describe experiments designed to test whether Met-tRNAf
is associated with either form. Our results indicate that (a) in the cell,
Met-tRNAf is bound to the native 40 S subunit, and in particular, to the
subunit of density 1.40 g x cm-3; (b) under the growth conditions used,
less than 10% of the low density native subunits have bound Met-tRNAf; (c)
the majority of the Met-tRNAf containing native 40 S subunits, isolated
from sucrose gradient analyses of cell extracts, join with 60 S subunits in
vitro to form 80 S monosomes only if additional ribosomal wash factors are
provided; and (d) the 80 S monosomes so formed are completed initiation
complexes that can form peptide bonds. These results support the hypothesis
that various forms of the native 40 S subunit represent different stages in
the formation of a complete initiation complex.