Dr Manishi Tripathi REVERSION SUPPRESSION Informational suppressors Interaction suppressors Overproduction suppressors Bypass suppressors Physiological suppressors ID: 1042689
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1. Microbial GeneticsLT-5Dr Manishi Tripathi
2. REVERSIONSUPPRESSION Informational suppressors Interaction suppressorsOverproduction suppressors
3. Bypass suppressors.Physiological suppressors
4. tRNA SuppressorsGenetic Detection of a Nonsense Suppressor
5. A particular UAG suppressor will not suppress all UAG chain termination mutations because the amino acid it inserts will not always produce an active protein. 2. Often the suppression is incomplete: The new proteins may have sufficient activity for colony formation, but the specific activity of the protein may be less than the wild-type protein. 3. A cell can survive the presence of a suppressor only if the cell also con¬ tains two or more copies of that tRNA gene. If there were only one copy of the tRNAsei gene and it was mutated so tRNAser recognized only the UAG codon, all normal UCG codons would be read as stop codons. There are, however, multiple copies of most tRNA genes, so in any living cell containing a suppressor tRNA, there will always be an additional copy of a wild-type tRNA that can function in normal translation
6. Normal Termination in the Presence of a Suppressor tRNA1.Protein factors active in translation termination respond to chain termi nation codons even when a tRNA molecule that recognizes the codon is present; thus suppression is weak. For example, if termination were sup¬ pressed only 10% of the time, the amount of the mutant protein made would be 10% of the wild-type, but 90% of other proteins would properly terminate. 2. Normal chain termination often uses pairs of distinct termination codons such as the sequence UAG-UAA. Thus, the existence of a UAG suppressor would not prevent termination of a double terminated protein.
7. Missense Suppressors(1) a mutant tRNA molecule may recognize two codons (2) a mutant tRNA molecule may be incorrectly recognized by an aminoacyl syn¬ thetase so it carries the wrong amino acid (3) a mutant aminoacyl synthetase may charge an incorrect tRNA molecule