Randomised library

Since it was first shown that functional nucleic acids could be selected from randomised libraries there have been many examples of aptamers and ribozymes selected for a variety of applications. There are a number of new reports on various aspects of aptamers, due in part to a special issue on this subject (Bioorganic and Medicinal Chemistry, 2001, volume 9, issue 10). Whilst most of the new aptamers that have been described are designed for binding to a given target, the number of aptamers that have catalytic activity is increasing. There are also examples now of allosteric aptamers, both for binding and with catalytic activity, that function only in the presence of a co-factor . 

The randomised nucleotide library that is used as the input in the initial selection procedure is conveniently generated on a DNA synthesiser and transcribed into an RNA pool by in vitro transcription. Designing the structure of the library is a crucial step which should be planned carefully. Three main types of libraries are in general use A fully randomised library a randomised region which is embedded in a natural RNA structure and a doped library where each position of a specific RNA sequence contains a... 

An additional consideration is the required level of library complexity and RNA length. Due to experimental limitations the pool of RNAs has a practical limit of approximately 1015 molecules. This corresponds to approximately the number of sequence combinations in a randomised 25-nucleotide long oligonucleotide (425 — 1015). However, for some applications it is desirable to ran-... 

A systematic review brings together and evaluates all the relevant research relating to a particular question. A group known as the Cochrane Collaboration has been formed for the purpose of appraising medical treatments and publish its finding in the Cochrane Library which is available, freely in some countries, on the internet. Most of the focus has so far been on evidence of efficacy from randomised trials but an adverse event methods group has recently been formed. 

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