Nitrogen is first limiting element 

TLS Online TPP Program

#Id: 2639

#Unit 13. Methods in Biology

Sometimes the S1 nuclease will not digest the single stranded regions completely, so the transcript appears to be a little longer than it really is, But another method, called primer extension, can tell the 5’-end (but not the 3’-end) to the exact nucleotide

TLS Online TPP Program

#Id: 2640

#Unit 13. Methods in Biology

Run-off transcription is a means of checking the efficiency and accuracy of in vitro transcription.

TLS Online TPP Program

#Id: 2641

#Unit 13. Methods in Biology

The size of this run-off transcript locates the transcription start site, and the amount of this transcript reflects the efficiency of transcription. 

TLS Online TPP Program

#Id: 2642

#Unit 13. Methods in Biology

Notice that S1 mapping and primer extension are well suited to mapping transcripts made in vivo; by contrast, run-off transcription relies on transcription in vitro.

TLS Online TPP Program

#Id: 2643

#Unit 13. Methods in Biology

After you have identified the physiological transcription start site by S1 mapping or primer extension you can use run-off transcription in vitro.

TLS Online TPP Program

#Id: 2644

#Unit 13. Methods in Biology

A variation on the run-off theme of quantifying accurate transcription in vitro is the G-less cassette assay.