A molecular biologist has discovered a new strain of bacteria that utilizes a sequence other than GATC to guide its mismatch repair activities. Which of the following sequences cannot be used by this new bacterium for mismatch repair?
The correct answer and explanation is :
The sequence that cannot be used by this new bacterium for mismatch repair is GGATC.
Explanation:
In molecular biology, the mismatch repair system (MMR) plays a crucial role in correcting errors that occur during DNA replication. In many bacteria, the repair system relies on recognition of certain DNA sequences that are methylated. For example, in Escherichia coli (E. coli), the sequence GATC is specifically recognized by the MutHLS mismatch repair complex. This system uses methylation of the adenine in the GATC sequence to distinguish between the newly synthesized strand and the template strand, which is already methylated. The MutS protein identifies mismatched base pairs, and MutH introduces a nick in the newly synthesized strand to initiate repair. The system relies on the methylation status of the adenine within the GATC sequence to recognize the strand that should be repaired.
Now, if the molecular biologist discovered a new strain of bacteria that uses a different sequence instead of GATC for mismatch repair, it means this strain could have a novel recognition sequence or mechanism. However, sequences like GGATC, which share some similarity with the GATC sequence but differ in key positions, would likely not be recognized as effectively or at all by the repair machinery. The specific recognition sites in the bacterial repair system are highly specific and typically require a sequence with exact or very similar nucleotide patterns. A substitution of just one nucleotide (such as GATC changing to GGATC) could prevent the system from correctly identifying the mismatch and, therefore, would not be functional for mismatch repair in this context.
In conclusion, GGATC does not align with the specialized recognition sequence of the bacteria’s mismatch repair system, making it an unlikely candidate for use in this bacterium’s repair mechanism.