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Fig. 10.1
In order to generate a cell-specific aptamer, the selection procedure can vary from tradi-
tional purified membrane protein-based SELEX (
a
) to live cell-based SELEX (
b
). Generally, in a
typical SELEX procedure, the initial single-stranded DNA/RNA pool contains a 20-60-nt random
sequence to provide a sequence space that facilitates presence of structures with high binding affinity
to the target protein. By repeating selection rounds, aptamers against any given targets can be rou-
tinely isolated from an initial combinatorial oligonucleotide library. (
a
) A typical puri fi ed protein,
membrane-based SELEX procedure consists of four main steps (1) binding to the target protein,
(2) selective partitioning, (3) recovery of target-bound sequences, and (4) re-amplification of recov-
ered species. (
b
) A live cell-based SELEX procedure also consists of four main steps: (1) counterse-
lection by incubating library with negative cells that do not express the target protein, (2) positive
selection by incubating recovered unbound sequences with positive cells expressing the target protein,
(3) recovery of target-bound sequences, and finally (4) re-amplification of recovered species
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