Question

The strain of XDR-TB that the young man had above was studied further by analyzing the DNA of the Mycobacterium tuberculosis. The investigators particularly looked at the gene for the protein targeted by the antibiotic rifampin. MDR-TB and XDR-TB are resistant to rifampin. Q1. What is the protein target for rifampin in the bacterial cells? What biological process does the antibiotic stop? (see notes). The following results were obtained from the young man's M. tuberculosis for the DNA sequence of the target gene of the rifampin antibiotic target. The normal gene sequence of the DNA coding strand is 5' AGC 3' which was changed (mutation) in this young man's DNA to 5 ATC 3 Q2. What are the two mRNA codons from these two DNA triplets? No other mutations were observed in the gene. This one mutation was the reason for the resistance in the young man's Mycobacterium tuberculosis to the rifampin.

Answer 1

1. The protein target for rifampin is DNA dependent RNA polymerase. Rifampin binds to the $\beta$ subunit of RNA polymerase and  inhibits its activity.

Rifampin is an antibiotic mostly used in the treatment of tuberculosis.

Rifampin inhibits the process of Transcription there by preventing RNA synthesis.

2. As we know , in RNA Thymine will be replaced with Uracil , the new mRNA codons will be

5^' AGC 3^' becomes UCG

5^' ATC 3^'   becomes UAG

3. Point mutation has occured because a single base is replaced by another base .

4. Before mutation the codon coded for SERINE ( UCG ) and after mutation it coded for a STOP CODON ( UAG).