The sequence below corresponds to the first 15 bases of the open reading frame of the E.coli cysS gene. For each of the following mutation sequences, determine the amino acid sequence encoded by the 15 bases, identify whether the mutation is a transition, transversion, insertion, deletion. Also identify whether the mutation is a missense, nonsense, silent or frame-shift mutation. 5\' ATG CTA AAA ATC TTC .... 5\' ATG CTA AAG ATC TTC.... 5\' ATG CTA TAA ATC TTC .... 5\' ATG CTA AAA AAT CTT 5\' ATG CGA AAA ATC TTC .... Consider the following normal sequence: Gly-leu-arg-gin-cys-ile-phe And the following mutant proteins. What is the nature of each mutation? Gly-leu-arg-gln Gly-leu-arg-arg-cys-ile-phe Gly-phe-lys-thr-met-gln-ile Do you consider TEs to be mutagens? Explain. Epidermolytic hyperkeratosis is an autosomal dominant condition that produces scaly skin. It can be caused by a missense mutation that substitutes a histidine (his) amino acid with an arginine (arg). Write the mRNA codons that could account for this change, and indicate if it is a transition or transversion.
Answer:
5. WT sequence: M L K I F
atg cta aaa atc ttc
a. Mutated sequence: M L K I F
atg cta aag atc ttc
Since the mutation (aaa to aag) codes for the same amino acid, Lys, it is a silent mutation. (Transition mutation at 9th position of the nucleotide sequence)
b. Mutated sequence: M L Stop
atg cta taa atc ttc
The mutation leads to a premature truncation of the product due to substitution of A to T at 7th position. So, its a non-sense mutation (Transversion mutation).
c. Mutated sequence: M L K N L
atg cta aaa aat ctt
The mutation leads to a frameshift in the reading frame due to a single nucleotide substitution (A) at 11th position. So, it is frameshift mutation (Insertion mutation).
d. Mutated sequence: M R K I F
atg cga aaa atc ttc
This mutation causes a single base substitution at 2nd amino acid position (T to G). So, it is a missense mutation (Transversion mutation).
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