19 - Transcription (Prokaryotes); Regulation of the Operons (2)

19 - Transcription (Prokaryotes); Regulation of the Operons (2)

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Plasmid can carry I gene as well…or only I gene (and not operon) Different combinations…. . Also combination of these mutation with mutations in structural genes (as products of structural genes ARE actually measured) J & M: Proof through complementation tests Transformation of the bacterial cells with plasmids carrying lac operon (whole or parts) - result is partially diploid cell – MERODIPLOID Purpose: artificially produced 2 sets of “alleles” for lac operon genes, complementation is enabled. Discovered/defined cis-elements and trans factors
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Genomic DNA: lacI - mutation – produced repressor cannot bind to operator – constitutive mutation; normal b gal always synthesized but plasmid carries normal lacI+ (However, plasmid carries mutated Z gene ) plasmids lacI + gene codes for a diffusible element that acts in trans by binding to any operator it encounters regardless of chromosomal location synthesis of normal b gal (coded by genomic DNA) will become regulated “Repair” of constitutive mutation lac I - *complementation in action* So, what is actually happening (step by step)?
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Genomic DNA Plasmid DNA lac absent Genomic DNA Plasmid DNA lac present RNAP binds…. from normal, genomic gene
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Non-inducible mutation lac I s Non-inducible lacI supperrepressor ( lacI s mutant) carried by plasmid can not bind inducer (lactose) All operator sites (O+) eventually occupied by superrepressor b gal (normal, coded by chromosome) will stop being produced lacI s mutant encodes a diffusible element that acts in trans by binding to any operator it encounters I mutations affect the expression of genes at both “chromosome” copies in “diploid bacteria” - I codes for the regulatory factor (repressor protein) which can diffuse (hence “ trans ”) throughout the cell and bind to operators regardless of their chromosomal location
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Constitutive mutation O c Constitutive lacI + product (repressor) cannot bind to O c b gal coded by chromosomal gene
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This note was uploaded on 12/23/2011 for the course BIOL 308 taught by Professor Miskovic during the Fall '09 term at Waterloo.

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19 - Transcription (Prokaryotes); Regulation of the Operons (2)

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