Correct option is B
The correct answer is (2) It has a mutation in RNAII (primer for replication initiation) and does not carry the rop gene.
Explanation:
The replication of ColE1-based plasmids like pUC18 is regulated by RNAI and RNAII. RNAII serves as the primer for replication initiation. A mutation in RNAII can lead to uncontrolled plasmid replication, causing an increase in plasmid copy number. Additionally, the rop gene negatively regulates plasmid replication. Without the rop gene, replication is less restricted, contributing to the high copy number seen in pUC18. Therefore, the high copy number in pUC18 is a result of the mutation in RNAII and the absence of the rop gene.
Information Booster:
RNAII is involved in the initiation of plasmid replication by serving as a primer.
A mutation in RNAII disrupts the regulation of replication initiation, leading to higher plasmid replication.
The rop gene normally limits plasmid replication, and its absence removes this control, leading to an increase in the plasmid copy number.
pUC18 is a high-copy-number plasmid due to the mutation in RNAII and the absence of the rop gene.
Mutations in RNAII and the absence of rop gene are essential for pUC18’s high copy number.
The regulation of replication in ColE1-based plasmids is a complex interaction between RNAII, RNAI, and rop.
Additional Information:
Option (1) is incorrect because the mutation in RNAI (antisense RNA) would affect replication regulation, but without a mutation in RNAII or the absence of the rop gene, it would not result in a high copy number.
Option (3) is incorrect because the mutation in RNAI alone is insufficient to cause a high copy number, and the overexpression of the rop gene would limit replication, contrary to the high copy number in pUC18.
Option (4) is incorrect because although a mutation in RNAII and overexpression of rop can affect replication, rop overexpression is typically associated with a decrease in plasmid copy number, not an increase.
