What is the meaning of conservation site in miRNA-mRNA pairing context?

Question

[Na Sed]

I am not biologist and just work in Bioinformatics field. Does anyone know what is the meaning of conservation in the context of miRNAs and their pairings to mRNAs?

Example:

Each of these duplexes has a region called the "seed", a site located at 5' part of miRNA (positions 2-7) which is characterized by a strict or almost strict Watson-Crick pairing between miRNA and its target site and shows the best conservation among the miRNA sequence.

(from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3182075/)

Answer 1

[David Langenberger]

That basically means that the seed seems to be very important for microRNA:mRNA binding. That results in the fact, that the seed region within the mature microRNA is highly (or higher) conserved as the rest of the mature sequence. Why? Because, it is needed for the target recognition. If there is a mutation in the seed, the microRNA cannot bind any more and that's in the worst case mortal. The rest of the mature sequence is just needed to keep the secondary structure intact and thus there are more mutations possible (-> less conserved).