LIFESCI 4 Lecture 12: vid 13

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22 May 2018

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Vid 13

Amber mutation

• Brenner studied mutations that control the head protein of T4 phage

• Amber mutation UAG

- WT protein has full length, mutant proteins vary & shorter

- Su-: suppressor E coli

- mutation can be suppressed by being grown on amber mutant

- when utat phage grow o WT E oli, they a’t grow

- but can grow on amber suppressor E coli -> full length

- host range mutant

• nonsense mutation: when grown on WT E coli, get short protein; when grown on

suppressor strain, get full length protein

• mutated Amber suppressor has a mutation in tRNA gene

• in WT E coli, tRNA tyrosine has AUG anticodon; in suppressor E coli, tRNA tyrosine has

mutation: AUG mutated to AUC -> base pair with UAG (stop codon) -> keep translating

• suppressor mutation: reverts phenotype of the first mutation

- first mutation is nonsense mutation in phage T4 head protein

- second mutation is mutation in anticodon of tRNA tyrosine Su-

- so ut 1 a’t grow o WT, ut a grow o Aer utatio

• also can have suppression to normal stop codons

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