What is the Difference Between T4 and T7 DNA Ligase?

T4 and T7 DNA ligases are both enzymes used in molecular biology techniques to join nucleotides by forming phosphodiester bonds between the 3' hydroxyl end of the sugar moiety and the 5' end of DNA molecules. However, there are differences between the two enzymes:

1. Sequence Bias: T4 DNA ligase has a relatively low sequence bias and high fidelity, while T7 DNA ligase is highly biased. The bias of T7 DNA ligase limits the number of fragments that can be assembled using this enzyme, making it a less ideal choice for certain applications like Golden Gate Assembly.
2. Mismatches: T4 DNA ligase has relatively low sequence bias and high fidelity, dominated mostly by G:T mismatches. In contrast, T7 DNA ligase has a higher overall fidelity than T4 DNA ligase at 25°C, with fewer mismatched products formed by T7 DNA ligase.
3. Optimum pH: The optimum pH for T7 DNA ligase lies in the range of 7.0 – 7.2, while the optimum pH for T4 DNA ligase is slightly different.
4. Fidelity and Ability: T7 DNA ligase has much greater fidelity and accuracy in carrying out its function due to its smaller size. T4 DNA ligase can ligate both fully Watson-Crick base-paired DNA and nicks, making it more active and versatile.

In summary, T4 DNA ligase is generally recommended for most routine molecular cloning applications due to its lower sequence bias and versatility, while T7 DNA ligase is known for its higher fidelity and accuracy. However, the choice of ligase depends on the specific requirements of the application, such as the need for high fidelity or the ability to assemble a large number of fragments.

Comparative Table: T4 vs T7 DNA Ligase

T4 and T7 DNA ligases are both enzymes used in molecular biology techniques to join nucleotides by forming phosphodiester bonds between the 3' hydroxyl end of the sugar moiety and the 5' end of the DNA strand. However, they have some differences in their properties and applications:

T4 DNA ligase is one of the first enzymes to be isolated from the T4 bacteriophage. It is known for its high ligation efficiency and substrate specificity, making it a widely used enzyme in molecular biology. On the other hand, T7 DNA ligase is a smaller protein produced by the T7 bacteriophage and is isolated by infecting E. coli cells. It has been reported to have higher overall fidelity than T4 DNA ligase at 25°C.