Transcription start point

In genetics and molecular biology, the transcription start point ( TSP ) is the first nucleotide of a transcribed DNA segment. In general, such a section of DNA is a gene . The TSP is used to define genes, as this limits it at the 5 'end . A gene can have several TSPs. If these are in the immediate vicinity (a few nucleotides difference) and are based on the same promoter , one sometimes speaks of the microheterogeneity of a TSP.

A TSP is defined by the first nucleic base that can be found stably in the transcribed RNA . Nucleotides that are removed immediately after initiation of transcription are not included. The cap structure of eukaryotic genes is also excluded.

The start-nucleotide is on the DNA the position +1 assigned to the immediately preceding situated nucleotide position -1 . For example, position -100 denotes a nucleotide which is exactly 100 nucleotides upstream of the TSP of the corresponding gene.

Methods for determining TSPs are, for example, primer extension , various RACE-PCRs and S1 mapping .

literature

• Rolf Knippers: Molecular Genetics. 8th revised edition. Georg Thieme Verlag, Stuttgart et al. 2001, ISBN 3-13-477008-3 .