Lecture.15.Fall.2013(1)

Coli strain b but not strain k12 crick et al induced

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Unformatted text preview: will lead to a shifting of the reading frame, disrupting all amino acids downstream of the mutation Example: Original frame ATG CAA TTG GCC AAA TTT GGG CCC Insertion ATG CAA TATG GCC AAA TTT GGG CCC New frame ATG CAA TAT GGC CAA ATT TGG GCC C Cracking The Genetic Code • Phage T4 with mutant rII genes can infect E. coli strain B but not strain K12 • Crick et al. induced single-base insertion and deletion mutations in the T4 rII gene, and then tested these mutants for growth in strain K12. Predictions • Two base codon • Three base codon – A single deletion or insertion will disrupt the reading frame – A single deletion or insertion will disrupt the reading frame – A second deletion or insertion nearby will restore the reading frame (revertant) – Reversion only if the second mutation is the opposite of the first (insertion/deletion) – Three mutations of the same type also leads to reversion Results Mutation(s) Protein Sequence Reverted? One bp insertion (+) Frameshift N/A One bp deletion (-) Frameshift N/A One +, one - (near) No change or small changes Yes Two + or...
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