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#transcription start site

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Transcription Basics

Transcription start site is denoted as

First ribonucleotide incorporated by RNA polymerase designated +1 corresponds to transcription start site where initiation complex transitions to elongation. Typically purine adenine or guanine favored. Numbering counts downstream as +2, +3 along transcribed region, while upstream sequences receive negative values -1, -2 without zero between. Such convention allows precise localization of promoter hexamers such as bacterial -10 box centered near -10 and eukaryotic TATA around -30. Position +1 experimentally mapped by primer extension, S1 nuclease, or RNA-seq 5' end detection, fundamental for p

Ref: Lodish Chapter 8: TSS denoted as +1 convention; Alberts Chapter 6 Promoter mapping numbering

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Transcription Basics

Upstream region is defined relative to

Genomic coordinate system anchors transcription start site as +1 at first incorporated nucleotide. Sequences extending toward 5' direction of coding strand opposite transcription are defined upstream, numbered negatively without zero, harboring promoters and enhancers. Downstream sequences lie beyond +1 toward direction polymerase travels. Defining upstream relative to transcription start site rather than translational start distinguishes transcriptional regulation from translational context, allowing mapping of bacterial -10, -35 elements and eukaryotic TATA box at fixed distances from initia

Ref: Berg Biochemistry Chapter 28: Promoter coordinate system upstream of TSS; NCBI Bookshelf Numbering relative to transcription start

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