| SELEX (System Evolution of Ligands by Exponential enrichment), which is a universally-applied method for spanning of aptamer from oligonucleotide pool as potential pharmaceutical and diagnostic agents, has been under development for more than a decade. SELEX technology provides an excellent opportunity to search for oligonucleotides binding to target and has an advantage over other known methods for ligands discovery, such as the small molecule combinatorial chemistry and phage-displayed antibody technique. SELEX can be essentially applied to any target and generate a large number of lead compounds very quickly, reducing much work and saving much time before animal testing. SELEX begins, with a large population of single-stranded nucleic acid molecules that is challenged with a specific task. Usually, the task is to bind to a purified protein, yet many other tasks have been successfully selected, including cell binding, peptide binding, small molecule binding, nucleic acid binding and catalysis of a variety of chemical reactions. A successful SELEX experiment requires the determination of a method for partitioning those nucleic acid molecules that have performed the task from those that have not. A pool of randomized RNA or single stranded DNA sequences was selected againstinterested targets. Several rounds of spanning lead to winning sequences with specific structure called 'aptamers', which are single-stranded nucleic acids that perform a specific function. Structures of aptamer complexes reveal the key molecular interactions conferring specificity to the aptamer-ligand association, including the precise stacking of flat moieties, specific hydrogen binding, and molecular shape complementarities. The oligonucleotide aptamers selected by SELEX process are superior in terms of higher affinity, specificity and stability. This technology has found a wide range of applications, yet little work has been reported on development of SELEX aptamers to interact infectious disease agents or their epitopes for either diagnosis or potential therapy with the exceptions of SELEX aptamers specific for HIV components and a selection model for autoclaved anthrax spores. And anti-Bacillus anthracis spores aptamers' research related with structures and functions is remaining urgently.In the present report, our aim is not only to establish a mold taking selection as anthrax spores for a target, but also to study the relationship between structures and affinities of SELEXed DNA aptamers to Bacillus anthracis spores. Meanwhile choosing the higher affinity aptamer as the detection molecules for Bacillus anthracis spores, we open a new throughway for a rapid detection of the pathogen microbiology used in the war.The research results showed that a custom synthesized 78mer random oligonucleotides DNA library (ca. 10l4~l5types of different DNA), containing 35 random nucleotides flanked by primer annealing sites, was chemosynthesized, and was subjected to 18 rounds of selection of 'binding-washing-separation-PCR amplifying' by using SELEX method against spores of Bacillus anthracis vaccine strain A.16R. There were totally 18 rounds of selection and after each 3 rounds a counter-selection was performed. Counter-selection was binding reaction between the PCR product from each three round and the microcentrifuge tube used in the selection process and Bacillus cereus spores to getting rid of thecomponents bound to the tube and those unspecific to anthrax spores. 15%PAGE electrophoresis analysis of PCR products from different selection rounds were showed that electrophoresis bands of the expected size got compact with the progress of SELEX rounds. An optimization strategy was carried out with annealing at 58-68癈 and 20-22 cycles to ensure complete elongation of the products. 'Hot star1 strategy, with adding Tap DNA polymerase at penetration temperature, was employed in the experiment. Selected products in each round were amplified through PCR with biotin-modified primers. The amplified product in each round to the spores was visu...
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