Ingham-2: V(D)J Recombination Flashcards
2 general mechanisms for generating different specificities of Abs and TCRs
combinatorial and junctional diversity
Germ-line theory
Ab diversity is generated by recombining separate DNA segments in germ-line of genome of B cells
Somatic mutation theory
Ab variable regions undergo mutation in B cells to generate many diff. Ab
What segments do light chains have?
V, J
What segments do heavy chains have?
V, D, J
Combinatorial diversity is?
Combining different V and J or V, D, and J segments to make many different kinds of heavy and light chains
What is combinatorial diversity also called?
V(D)J recombination
2 factors that contribute to combinatorial diversity
- VDJ and VJ recombination
- combining of heavy and light chains
What is RSS?
Recombination Signal Sequence
What sequence is conserved in RSS?
heptamer-spacer-nonamer
Size of nucleotides spacer?
12 or 23bp
What is the 12/23 rule?
RSS with 12bp spacers can only recombine with RSS with 23bp spacers
What spacer is in 3’ of V-kappa?
12bp RSS
What spacer is in 5’ of J-kappa?
23bp RSS
What spacer is in 5’ and 3’ of D segment?
12bp
What spacer is in 3’ of VH?
23bp
What spacer is in 5’ of JH?
23 bp
RAG-1/2 protein function
- catalyze DNA strand breakage
- required for VDJ recombination
Function of Artemis?
- nicks hairpin made during recombination at one spot
How is junctional diversity made? (light chain)
Nicks made by Artemis are fixed by adding P (Palindromic) nucleotides
How is junctional diversity made in heavy chains? (x2)
- exonuclease trimming
- addition of N (non-templated) NTs by
What are exonucleases that can perform exonuclease trimming? (x2) (heavy chain)
- Artemis
- Rag proteins
What add N NTs on heavy chains?
TdT (terminal deoxynucleotidyl transferase)
What is the major target of combinatorial/junctional diversity?
CDR3
Does somatic hypermutation happen in T cells?
No
