You are cloning a gene from Candida albicans that you want to express in E. coli

Question

You are cloning a gene from Candida albicans that you want to express in E. coli for purification. You want the E. coli cells to make a protein with the exact amino acid sequence as in Candida albicans. How could you mutate the DNA sequence of your gene of interest to ensure that the 5-CUG-3 codon codes for serine for instead of leucine?

Check all that apply.

- change every in-frame 5'-CUG-3' to 5'-UCG-3'

- change every in-frame 5'-CUG-3' to 5'-UCC-3' - change every in-frame 5'-CUG-3' to 5'-AGU-3' - change every in-frame 5'-CTG-3' to 5'-AGT-3' - change every in-frame 5'-CTG-3' to 5'-TCG-3' - change every in-frame 5'-CTG-3' to 5'-TCC-3'

Explanation / Answer

Choice 1 is correct (change every in-frame 5'-CUG-3' to 5'-UCG-3)

Reason: According to the amino acid codon sequences, every amino acid is encoded by one or more codon sequences which are specific to that amino acid. This means that every time that particular codon sequence arrives in the gene, it will indeed encode for that particular amino acid. For example, the codon CUG encodes to amino acid leucine wherease the codon UCG encodes for amino acid serine. Thus, in order to change the sequence of an organism such that it produces amino acid serine instead of leucine, all the in-frames or the coding sequences of the gene for amino acid leucine must be replaced with the codon of amino acid serine i.e. UCG. Importantly, this change must be brought in 5' to 3' direction because transcription and translation take place only in 5' to 3' direction.

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