Ligase Chain Reaction

Kevin O'Donnell odonnell at sasa.gov.uk
Mon Mar 27 04:21:42 EST 1995


In article <3kvmqt$l1a at deep.rsoft.bc.ca>, Donald Lee 
<don_lee at mindlink.bc.ca> says:
>
>Can anyone be kind enough to explain what is a Ligase Chain Reaction?
>Be technical if you like.  Just happened to be out of science for a few 
years:-(
>Thank you in advance.

I'll have a go.

LCR is a nucleic acid amplification method that uses 2 pairs of 
complimentary probes.  Probes 1 and 2 are designed to anneal to target 
DNA immediately adjacent to one another.  The 'nick' between them is 
recognised by DNA ligase and ligated, so that 2 oligomers of e.g. 25 nt 
become one 50nt oligo.  The mixture is then heated so that the probe and 
target DNA are separated.  On cooling, further copies of probes 1&2  
can anneal to the target and probes 3&4 can anneal to the ligation product 
of probes 1&2, formed in the last round. 

The use of a thermostable ligase means that you can go through succesive 
round of denaturing/annealing/ligation. The end result is the exponential 
generation of 50nt ligation products from 25 nt probes. The advantages to 
this system are that it is sensitive to single base pair changes in the target 
and that it has to potential for automated detection through labelling of the 
probes.   

Useful references are:

Barany, F. 1991 Genetic disease detection and DNA amplification using 
cloned thermostable ligase Proc. Nat. Acad. Sci. 88:189-193

(the original LCR paper)

and a recent review:

Wiedmann et al. 1994 ligase chain reaction (LCR) -overview and 
applications PCR Methods and Applications 3:S51-S64


Hope this is helpful - it's a lot clearer when you've got a diagram in front 
of you!

Kevin O'Donnell
Scottish Agricultural Science Agency    
Edinburgh
Scotland                                           



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