J. Biol. Chem., Vol. 261, Issue 27, 12593-12595, 09, 1986
Protein synthesis in yeast. Identification of an altered elongation factor in thermolabile mutants of the yeast Saccharomyces cerevisiae
A Kamath and K Chakraburtty
Cell-free extracts from the wild type yeast strain (A364A) and from a group
of noncomplementing mutants that are conditionally defective in translation
were preincubated at a restrictive temperature prior to incubation at a
permissive temperature for protein synthesis. Results of these experiments
showed that upon exposure to the restrictive temperature (39 degrees C),
all five of the noncomplementing mutants lost ability to incorporate amino
acid into protein. The wild type parent strain retained better than 80% of
the activity under identical conditions of heat treatment. Mutant extracts
could be revived to incorporate amino acid by the addition of the purified
yeast elongation factor 3. Factors 1 and 2 had no effect. The heat-treated
extract from one mutant did not supplement the activity of the other
mutant. Although all five of the mutants were inactivated by preincubation
at 39 degrees C, each showed a variable rate and extent of thermolability.
Heat-treated mutant extracts were fully active in polyphenylalanine
synthesis with liver ribosomes but not with the yeast ribosomes. Since
liver ribosomes do not require factor 3, this assay then confirms that
factor 3 is the thermolabile component in this group of noncomplementing
mutants.