Biology Reference
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22
Some of the longer D-minigenes may have, in their coding regions, a short
segment similar to the 7-mer of the recombination signal sequence. In
certain cases, therefore, such D-minigenes can then join onto another D-
minigene, giving rise to longer nucleotide sequence for coding (Fig. 1-13).
Indeed, some of the longer CDRH3 sequences consisted of D-D joining
(Kurosawa and Tonegawa, 1982), and even D-D-D joining. The
combination of all of the above mentioned mechanisms of generating coding
regions for CDRH3 can in fact result in thousands, millions or even billions
of different sequences of varying amino acid residues and lengths. It has
thus been suggested that CDRH3 alone is sufficient to define the fine
specificity of an antibody. The other five CDR's would improve the overall
binding affinity of the antibody.
Figure 1-13. The mechanism of D-D joining.
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