A translated reading region upstream of a main coding region in a messenger RNA. Its effects depend on initiation, termination, scanning and reinitiation, rather than its mere presence.
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An upstream open reading frame (uORF) is a non-canonical feature found in the messenger RNA (mRNA) of eukaryotic genes that can regulate gene expression. It is called "upstream" because it is located upstream (5' region) of the main coding sequence of a gene that encodes the primary protein product.