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Section: Genetics » Regulation of Gene Expression » Operon Circuits in Prokaryotes
 
 
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  Identification of starting point
 
     
 
Content
⇒ Regulation of Gene Expression 1.  Operon Circuits in Bacteria and other Prokaryotes
⇒ Induction and repression
⇒ Inducer and co-repressor
⇒ The operon model for transcriptional regulation 
⇒ The tryptophan operon in bacteria (E. coli and Salmonella)
⇒ Tryptophan (trp) repressor controls three sets of genes
⇒ Negative and Positive Controls of Transcription
⇒ Substitution of Sigma Factor and Control of Transcription
⇒ Multiple sigma factors in E. coli 
⇒ Sporulation in bacteria
⇒ DNA sequences controlling transcription 
⇒ DNA sequences for CAP, RNA polymerase and lac-repressor
⇒ Identification of starting point
⇒ Pribnow box and other sequences common to DNA regions upstream to several operons
⇒ Regulation by DNA rearrangements
⇒ Post-transcriptional regulation
⇒ Leader sequences and attenuators
⇒ Autogenous regulation of translation
⇒ Regulation by alternative splicing
⇒ Regulation by-anti-sense RNA
⇒ Repression and activation of translation
⇒ Feedback inhibition
⇒ Signal transduction and ‘two component regulatory system’
Identification of starting point
In the DNA segment sequenced as above, starting point of transcription in 'lac' operon could be identified with the help of S1 nuclease. This enzyme has the ability to degrade single stranded DNA or RNA, but not DNA-RNA hybrids. Therefore, a DNA restriction fragment (obtained due to treatment with a specific restriction endonuclease) containing the starting point and some transcription region of DNA, was hybridized with excess of lac mRNA (5' end of mRNA will be complementary to startpoint in DNA) and then digested with S, nuclease. The size of protected duplex DNA-RNA hybrid will determine the position of starting point (upstream) from the downstream restriction site. This sequence used as starting point is shown in Figure 35.21.

Nucleotide sequence of DNA in E. coli lac transcription control regions, showing functions of different regions and the effects of mutations in these regions.
Fig. 35.21. Nucleotide sequence of DNA in E. coli lac transcription control regions, showing functions of different regions and the effects of mutations in these regions.

 
     






     
     
 
 
     
 
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