The T-cell receptor ?-chain locus can undergo successive gene rearrangements to rescue unproductive V(D)J rearrangements
A. What aspects of gene segment rearrangement at the TCR? locus make this possible?
B. Can the immunoglobulin heavy-chain locus, which is also composed of V, D, and J segments, undergo successive rearrangements? If not, give the reasons for the difference.
A. Successive gene rearrangement is possible at a TCRβ locus because there are two sets of D, J, and C gene segments downstream of the cluster of V gene segments: (Vβ)n…Dβ1…(Jβ1)n…Cβ1…Dβ2…(Jβ2)n…Cβ2. If a first rearrangement involving Dβ1 and a Jβ1 segment is unproductive, an upstream V gene segment can rearrange to the second D gene segment and an associated J segment. If this is unproductive, no more rearrangements can be made.
B. The answer is no. The heavy-chain locus has the following configuration: (V)n-heptamer…23 spacer…nonamer…nonamer…12 spacer… heptamer-(D)n-heptamer…12 spacer…nonamer…nonamer… 23 spacer…heptamer (J)n…Cμ. After the first DJ rearrangement, the intervening D segments between the chosen D and J will be deleted. After VDJ rearrangement, the D segments that lie between the chosen V and DJ will be deleted. Therefore, no unrearranged D segments remain after these two rearrangement events. V and J cannot rearrange directly because the recombination signal sequences are not paired appropriately and do not follow the 23/12 rule; rather, they both contain 23-bp spacers in their recombination signal sequences. Successive gene rearrangement is thus not possible at a heavy-chain locus.
You might also like to view...
Which of the following food items are considered an important dietary source of vitamin D? Select all that apply
A) Fish B) Cottage cheese C) Irradiated milk D) Mozzarella cheese sticks E) Apples
The formula for density is ____.
A. weight ¸ volume B. area ¸ volume C. volume ¸ surface area D. weight ¸ surface area
Gonorrhea is a fungal infection.
Answer the following statement true (T) or false (F)
Health education specialists can assist both patients and medical organizations by
A) helping patients understand their options. B) providing services to individuals who do not have insurance. C) restructuring the health care system. D) increasing funding for prevention education.