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Nullomers
Nullomers are short sequences of DNA base pairs that do not occur in the genome of a species (commonly humans), even though they are theoretically possible.〔 〕 Nullomers must be under a selective pressure - for example, they may be toxic to the cell.〔 They may be useful for treating cancers. Some nullomers have been shown to be useful to treat leukemia, breast, and prostate cancer. They are not useful in healthy cells because normal cells adapt and become immune to them.〔 Nullomers are also being developed for use as DNA tags to prevent cross contamination when analyzing crime scene material.
==Background==
Nullomers are naturally available amino acids, but potentially unused sequences of DNA. Determining these "forbidden" sequences can improve the understanding of the basic rules that govern sequence evolution. Sequencing the entire genome has shown that there is a high level of non-uniformity in genomic sequences. When a codon is artificially substituted for a synonymous codon, it often results in a lethal change and cell death. This is believed to be due to ribosomal stalling and early termination of protein synthesis. (For example: When substituting AGA for CGA in bacteria, both of which code for Arginine, you would think that would not make a difference. However, bacteria almost never use AGA, and when substituted it proves lethal.) Such codon biases have been seen in all species, and are examples of constraints on sequence evolution. Other sequences may have selective pressure, for example GG-rich sequences are use as sacrificial sinks for oxidative damage because oxidating agents are attracted to regions with GG-rich sequences and then induce strand breakage.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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