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.