Question

What protein products would be made by the mutant gene in the prescence of each of the following tRNAs:

-Serine-inserting amber [UAG] suppressor?

-Tyrosine-inserting ochre [UAA] suppressor?

-Glutamine-inserting opal [UGA] suppresor?

wild-type = mutant = UUA. AGC CUA AAU GAA AAU AGG, . 5 ' 3' 3 T 5' UUAAGC CCU AAA UGA AAA UAG G 3"

Answer 1

The three codons UAG (Amber), UAA (Ochre), and UGA (Opal) are usually translation termination signals. Three proteins, called release factors, are also required for termination. Release Factor 1 is required for termination at UAG and UAA codons, release factor 2 is required for termination at UAA and UGA codons, and release factor 3 accelerates the release of ribosomes from the mRNA. Cells contain about 1 molecule of release factor per 5 ribosomes.

Nonsense suppressors. Nonsense suppressors are produced by base substitution mutations in the DNA corresponding to the anticodon of a tRNA that cause the anticodon to pair with one of the terminarion (or "nonsense") codons, UAG (Amber), UAA (Ochre), or UGA (Opal). Examples of nonsense suppressors produced by single base substitutions in E. coli are shown in the following table. Note that because of the wobble rules amber suppressing tRNAs can only read UAG codons, but ochre-suppressing tRNAs can read both UAA and UAG codons.

Serine-inserting amber [UAG] suppresso :leu-ser-pro-lys-trp-lys-stop

Glutamine-inserting opal [UGA] suppresor : leu-ser-pro-lys-stop

-Tyrosine-inserting ochre [UAA] suppressor : leu-ser-pro-lys-trp-lys-stop