| upstream | <molecular biology> Refers to nucleotide sequences that precede the codons specifying the mRNA or that precede (are on the 5' side of) the protein coding sequence. Also used of the early events in any process that involves sequential reactions. (18 Nov 1997) |
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| upstream activation site | A DNA sequence that regulates transcription like an enhancer but does notwork if its located downstream from a promoter. (09 Oct 1997) |