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sigma subunit + core enzyme, binds to promoter, unwinds DNA, begins polymerization of bases complementary to DNA template
Rho dependent Termination
Rho factor recognizes sequence in mRNA, binds to it, and pulls it away from RNA polymerase
Rho independent Termination
stem loop structure formed by sequence of 20 bases with a run of 6 or more U signals release of RNA polymerase
for translation signal ribosomes to bind near 5' end of mRNA while downstream transcription is still occuring
often leads to the translation of several genes at the same time from one mRNA transcript
regulation of gene expression
1. binding of RNA poly to promoter 2. shift from initiation to elongation 3.release of mRNA at termination 4.posttranscriptional stability of mRNA
5. efficiency of ribosomes to recognize translation initiation sites 6.stability of polypeptide product
Single signal can simultaneously regulate expression of several genes that are clustered together on a chromosomes and involve the same process.
trans acting elements
can diffuse through cytoplasm and act at target DNA sites on any DNA molecule in cell ( repressor)
cis acting elements
(operator site) can only influence expression of adjacent genes on same DNA molecule
In absence of lactose, repressor binds to operator which prevents transcription, negative regulatory element
if there is no lactose in cell, a ____is bound to operator Z, Y, and A genes can't be expressed
1. allocation binds to repressor 2. repressor changes shape and cannot bind to operator 3. RNA poly binds to promoter and initiates transcription of polycistronic RNA
normal repressor end can bind to operator or normal inducer end, if inducer can bind to repressor, repressor cannot bind lacA, Y and Z are transcribed
mutant repressor cannot bind to operator, operator end of repressor deformed enzyme produced constitutively
superrepressor mutant repressor, inducer can not bind to repressor, repressor can bind to operon even when inducer are present, enzyme are not produced
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