DNA recombination -
- an example of gene translocation is the antigen receptor gene in the vertebrate immune system
- in B lymphocytes, DNA recombination (aka VDJ joining) leads to the expression of one particular variable (V) region gene for each
immunoglobin (Ig) light- or heavy-chain gene
- in the Ig k light-chain genes, there are >300 germline V segments and one constant (C) gene locus containing 4 joining (J) segments
and an enhancer region
- once the B cell has picked its AB, it proliferates many clones of the same antibody and we can fight off the immune attack
what are variable regions, it is random
- in the chromosome in the B cell, this is where its happening, a permanent excision of this part of the DNA
- the ones that aren’t good, die
- promoter sequence and enhancer (drives expression, in the intron, between variable and constant domain)
- DNA deletion brings a promoter carried by each V gene segment and the enhancer region b/w the J and C gene segments into
proximity, thus activating the translocated gene
Gene Conversion -
- this is another gene-translocation mechanism that activates one particular member of the multigene family (found in yeast mating-type choice and antigenic variation in African trypanosomes)
(- chicken Ig and T-cell receptor genes use gene conversion for their expression and diversification)
- the cell makes a copy of the gene and inserts it into an expression casette
- a copy of the gene to be activated is transferred into the expression cassette located remotely from the gene cluster
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