Question

If this is the end of the V sequence, where will be Rag-1/Rag-2 cleavage?

V(kappa)-A-T-C-A-G-T-c-a-c-a-g-t-g-T-A-G-T-C-A-g-t-g-t-c-a-c-

a) After the first T
b) After the second T
c) After the third T
d) After the fourth T

Answer 1

The Rag-1/Rag-2 cleavage will occur after the third T. Thus the correct option is C.

Step-by-step explanation:

In V(D)J recombination, Rag-1 and Rag-2 enzymes are responsible for cleaving DNA sequences at specific sites, facilitating the rearrangement of immunoglobulin and T-cell receptor genes. The sequence provided seems to represent a V segment of the immunoglobulin gene. The Rag-1/Rag-2 cleavage occurs at conserved sequences known as recombination signal sequences (RSS). These RSS sites are composed of a conserved heptamer and a conserved nonamer separated by a less conserved spacer region.

In the sequence provided, the conserved heptamer sequence is represented by the sequence TGTG, which appears three times - "T-G-T-G" is present after the third T in the sequence. The Rag-1/Rag-2 complex recognizes these heptamer sequences for cleavage. Therefore, the cleavage would occur after the third T, following the recognition of the third heptamer sequence "TGTG."

Understanding the location and nature of these conserved sequences is crucial in predicting where the Rag-1/Rag-2 cleavage will take place during V(D)J recombination. In this case, the recognition and cleavage site are determined by the presence of the conserved heptamer sequences, specifically the third occurrence of the TGTG sequence in the provided sequence. Thus the correct option is C.