Fj. Trianaalonso et al., THE ELONGATION-FACTOR-3 UNIQUE IN HIGHER FUNGI AND ESSENTIAL FOR PROTEIN-BIOSYNTHESIS IS AN E-SITE FACTOR, The Journal of biological chemistry, 270(35), 1995, pp. 20473-20478
Two elongation factors drive the ribosomal elongation cycle; elongatio
n factor 1 alpha (EP-1 alpha) mediates the binding of an aminoacyl-tRN
A to the ribosomal A site, whereas elongation factor 2 (EF-2) catalyze
s the translocation reaction. Ribosomes from yeast and other higher fu
ngi require a third elongation factor (EF-3) which is essential for th
e elongation process, but the step affected by EF-3 has not yet been i
dentified. Here we demonstrate that the first and the third tRNA bindi
ng site (A and E sites, respectively) of yeast ribosomes are reciproca
lly linked; if the A site is occupied the E site has lost its binding
capability, and vice versa, if the E site is occupied the A site has a
low affinity for tRNAs. EF-3 is essential for EF-1 alpha-dependent A
site binding of amino acyl-tRNA only when the E site is occupied with
a deacylated tRNA. The ATP-dependent activity of EF-3 is required for
the release of deacylated tRNA from the E site during A site occupatio
n.