Q.34 Consider the following statements:

I. T4 DNA ligase can catalyze blunt end ligation more efficiently than E. coli DNA ligase.
II. The ligation efficiency of T4 DNA ligase can be increased with PEG and ficoll.

Options:

(A) Only I is true

(B) Both I and II are true

(C) Only II is true

(D) I is true and II is false

T4 DNA ligase excels in blunt end ligation compared to E. coli DNA ligase, making it essential for molecular cloning. Both statements in the query hold true, with PEG boosting T4 efficiency.

Correct Answer

The right option is (B) Both I and II are true.
T4 DNA ligase catalyzes blunt end ligation far more efficiently than E. coli DNA ligase, which struggles with non-cohesive ends. Adding PEG or ficoll further enhances T4’s performance by crowding macromolecules and stabilizing complexes.

Statement I Analysis

T4 DNA ligase efficiently joins blunt-ended DNA fragments, unlike E. coli DNA ligase, which primarily handles cohesive (sticky) ends from restriction enzymes.
E. coli ligase shows poor or negligible activity on blunt ends under standard conditions, requiring NAD+ cofactor versus T4’s ATP.
This difference stems from T4’s origin in bacteriophage T4, enabling versatile ligation in cloning workflows.

Statement II Analysis

PEG (polyethylene glycol) and ficoll increase T4 DNA ligase efficiency by volume exclusion, promoting DNA strand alignment.
Studies confirm PEG boosts blunt end ligation up to 72.8% efficiency, outperforming standard conditions at 58.2%.
Ficoll acts similarly as a crowding agent, ideal for low-concentration DNA in biotech experiments.

Option Breakdown

Practical Applications

Use T4 for blunt or sticky end cloning, adding 5-10% PEG for tough ligations in vectors like pUC19.
E. coli ligase suits high-salt, cohesive-end needs but avoid for blunt work.
For exams or labs, remember: T4 versatility + crowding agents = optimal results.