Long primers forms most probably dimers, so taq pol amplifying this (in low temp) also.

TLS Online TPP Program

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#Unit 13. Methods in Biology

In Run-on transcription- the RNA polymerase that has already initiated transcription in vivo simply “runs on” or continues to elongate the same RNA chains. 

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#Unit 13. Methods in Biology

The run-on reaction is usually done in the presence of labeled nucleotides so the products will be labeled.

TLS Online TPP Program

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#Unit 13. Methods in Biology

Nuclear run-on transcription is a way of ascertaining which genes are active in a given cell by allowing transcription of these genes to continue in isolated nuclei.

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#Unit 13. Methods in Biology

The run-on assay can also be used to determine the effects of assay conditions on nuclear transcription.

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#Unit 13. Methods in Biology

To measure the activity of a promoter, one can link it to a reporter gene, such as the genes encoding b-galactosidase, CAT, or luciferase, and let 

the easily assayed reporter gene products indicate the activity of the promoter.

TLS Online TPP Program

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#Unit 13. Methods in Biology

You can use S1 mapping or primer extension analysis to do this measurement, but you can also substitute a reporter gene for the natural gene, and then assay the activity of the reporter gene product.