Transcription and RNA Processing

ID #1159

What does it mean to say a site is conserved and has a consensus sequence?

"Conserved" means that if you compare a particular sequence in a variety of different organisms, or perhaps a sequence that is found in a number of different places within a single organism, that sequence has little variation despite the evolutionary differences in organisms or differing roles within that single organism. As an example, if you compare the promoter sequences (the -10 and -35 sites) for 100 different genes in E. coli, you will find that the -10 site is pretty close to TATAAT in all 100 genes. Not all 100 of them will be exactly TATAAT, but they'll all be close. One may be TGTAAT, and another one TATTAT, and so on, but if you "average" them out, the consensus sequence is TATAAT. That makes this sequence highly conserved, since it doesn't differ much from one promoter to the next.

So to summarize, a conserved sequence is a more general term that could be referring to a promoter, or a ribosome binding site, or an origin of replication, or the amino acid sequence of histone proteins, etc. Within a given conserved region, you can determine specifically what bases or amino acids are likely to be there most of the time, and that is the consensus sequence of that particular conserved region.

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