VDJ recombination Ch:8 176-186 Flashcards
Elucidate
To explain something. Make something clear.
What is the difference between heavy and light chains?
Heavy chains have V, D and J regions, while light chains only have V and J regions
Nascent
Just coming into existence and beginning to display signs of future potential
What are the two Ig Light chains?
K (kappa) or lambda chains
CDR3
Complementarity-Determining region 3, Hypervariable. Junctional region between the V and D segments as well as the sequences of the D and J themselves. Occurs as a results of junctional diversity.
What chains lack D regions, including TCRs?
Ig Light chains and TCR alpha and gamma
What chains have D regions, including TCRs?
Ig heavy chains, TCR beta and sigma
RSS (Location, Components, )
Recombination signal sequences. located 3’ of each V gene, 5’ of every J segment, flanks every side of D segment. Contains a heptamer (CCAGTG), a spacer 12 or 23 non conserved nucleotides (correspond to 1-2 turns of the DNA helix, and a highly conserved AT rich stretch o 9 nucleotide spacers.
The 12/23 Rule
The phenomenon that recombination only occurs between two segments only if one of the segments is flanked by a 12-nucleotide spacer and the other is flanked by a 23-nucleotide spacer.
Why can’t V to J recombination occur in heavy chains?
Because V chains and J chains are both flanked by 23 nucleotide spacers, which would be a direct violation of the 12/23 rule
What are the four distinct events of VDJ recombination?
1) Synapsis ( looping of segments and their two flanking regions) 2) Cleavage (Double stranded breaks produced by RAG-1/2) 3) Hairpin opening and end processing (Artemis opens the hairpins at coding ends; TdT adds base to broken DNA ends 4) Joining (via nonhomologous end joining; Ku70, Ku80, DNA-PK, DNA ligase IV and XRCC4)
VDJ Recombinase
Complex made up of RAG-1 and RAG-2. (Recombination-activating gene 1) RAG-1 recognizes the DNA sequence at the junction between a heptamer and a coding segment and cleaves it, but is only active in the presence of RAG-2
Artemis
an endonuclease that opens up the hairpins at the coding ends.
Endonuclease
an enzyme that cuts DNA at or near a specific recognition nucleotide sequences known as restriction sites.
TdT
Terminal deoxynucleotidyl transferase. Adds bases to broken DNA ends.
Ku70 and Ku80
DNA end-binding proteins that binds to the breaks and recruit the catalytic subunit of DNA-dependent protein kinase (DNA-PK)
DNA-PK
Double stranded DNA repair enzyme
What two compounds are used to ligate processed broken ends?
DNA Ligase IV and XRCC4
Combinatorial Diversity
VDJ rearrangement brings together multiple germ line gene segments that may combine randomly, and different combination produce different antigen receptors
Junctional Diversity
Diversity generated by the addition or removal of nucleotides at the junctions of the V and D, D and J, or V and J segments.
