Question

In immunoglobulin (IgG) heavy chain gene rearrangements, the Rag proteins are able to cut the DNA so that V cassettes are only joined to D cassettes, and not to J cassettes. How is this specified?

1.Rearrangement can only occur between a pair of signal sequences that are separated by a 23 bp spacer and a 12 bp spacer, respectively.
2. RAG proteins recognize the 3' splice site of a V domain exon and can only join it to the 5' splice site of a randomly selected D exon.
3. RAG protein makes cuts within recombination signal sequences, 7 and 9 base pairs long, which must be present in reverse orientation in the joined segments.
4. Rearrangement removes all of the unused V, D, and J gene segments.
5. None of the choices are correct

Answer 1

Answer: 1 Rearrangement can only occur between a pair of signal sequences that are separated by a 23 bp spacer and a 12 bp spacer respectively.

For immunoglobulin (IgG) heavy chain gene arrangements, is based on 12/23 rule. it occurs between gene segments located on the same chromosome. Gene segments flanked by a RSS( Recombination signal sequence) with 12 base pair (bp) spacer can be joined to 23 base pair spacer.

In this chain arrangement, VH gene segment can only join to JH gene segment directly because both are flanked by 23 bp Spacers and DH gene segment has 12 bp spacer on both side.