Transcription Initiation Frequency for the Tryptophan Operon of Escherichia coli

  1. Ron Baker and
  2. Charles Yanofsky
  1. Department of Biological Sciences, Stanford University, Stanford, California

This extract was created in the absence of an abstract.

Excerpt

We have been attempting to determine the absolute number of trp messenger RNA (mRNA) molecules in cells of Escherichia coli grown under various states of derepression. We have approached this problem by labeling trp mRNA with 3H-uridine under conditions where the specific activity of the UTP and CTP pools could be assumed. This was achieved by employing a pyrimidine-requiring mutant which cannot synthesize uridine or cytidine and is therefore dependent upon exogenously supplied pyrimidines as precursors for RNA synthesis. By growing such a strain for several generations in the presence of 3H-uridine the pyrimidines in all RNA molecules will have the same specific radioactivity as the added uridine. Hybridization of the trp mRNA isolated from such cultures under conditions where the efficiency of hybridization of trp mRNA is between 90 and 100 % permits a quantitative determination of the amount of trp mRNA in a sample of RNA extracted from...

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