Fidelity of protein synthesis depends to a large extent on the accuracy of aminoacylation of tRNAs with correct amino acids. However, given that the side chains of many amino acids are not sufficiently different, aminoacyl-tRNA synthetases (aaRS) are often prone to misacylate the tRNAs. One such example of misacylation is of tRNA^Thr by ThrRS. In this context, following statements are being made about E. coli ThrRS:

A. It misacylates tRNA^Thr equally with Ser and Thr.
B. It possesses a distinct editing site that preferentially deactivates the misacylated tRNA^Thr.
C. The editing of the misacylated tRNA^Thr occurs frequently in cis before the release of the misacylated tRNA^Thr.
D. It possesses a distinct editing site that does not discriminate between the misacylated tRNA^Thr and Thr-tRNA^Thr.
E. The aminoacylation and the editing sites of ThrRS are the same.
Choose the option that represents all correct statements.

Correct option is B

Explanation-

Statement A - It misacylates tRNA^Thr equally with Ser and Cys.
This statement is Incorrect. ThrRS is known to misacylate tRNA^Thr more commonly with serine than with cysteine, but not equally.

Statement B - It possesses a distinct editing site that preferentially deacylates the misacylated tRNA^Thr.
This statement is Correct. ThrRS has a proofreading/editing domain that hydrolyzes incorrectly charged tRNA^Thr (e.g., Ser-tRNA^Thr or Cys-tRNA^Thr).

Statement C - The editing of the misacylated tRNA^Thr occurs frequently in cis before the release of the misacylated tRNA^Thr.
This statement is Correct. In many aaRSs, including ThrRS, editing typically occurs in cis—i.e., the mischarged tRNA is edited before it is released from the enzyme.

Statement D - It possesses a distinct editing site that does not discriminate between the misacylated tRNA^Thr and Thr-tRNA^Thr.
This statement is Incorrect. The editing site specifically discriminates to prevent hydrolysis of correctly acylated Thr-tRNA^Thr, allowing only misacylated species to be hydrolyzed.

Statement E -  The aminoacylation and the editing sites of ThrRS are the same.
This statement is Incorrect. These are distinct functional domains: the aminoacylation site attaches the amino acid, while the editing site removes incorrect ones.

Since the correct statements is B and C
So, the correct answer is option b - B and C