MBB331_Week11-Fall-2011

Operon subunits of in rif rna polymerase not

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Unformatted text preview: n rRNA available r-proteins When bind rRNA, not their own rbind protein mRNA When no rRNA is available When unbound r-proteins accumulate and bind their own mRNAs inhibits further rmRNAs protein synthesis Not all genes in these operons Not regulated by R-protein binding regulated Examples: – in α operon, α subunit of RNA in polymerase not regulated polymerase – in rif operon, β subunits of in rif RNA polymerase not controlled by L10 r-protein but by their own autogenous regulation own α operon operon A Lewin Genes VII 2000 Oxford University Press 36 (ii) TRANSLATIONAL CONTROL: access to initiation sequences • RNA phages translation of one cistron requires translationinduced changes in preceding cistron… cistron initiation requires RNA structure changes by ribosome binding preceding cistron Lewin Genes VII 2000 Oxford University Press 37 (ii) TRANSLATIONAL CONTROL: access to initiation sequences • e.g. MS2 phage replicase gene translation is dependent on coat gene expression 38 (ii) TRANSLATIONAL CONTROL: access to initiation sequences • thiM gene encodes an enzyme required for thiaminesynthesis • 5´ end of thiM mRNA contains a riboswitch whose aptamer binds thiamine pyrophosphate (TPP) • -when TPP levels are high, the cell doesn’t want to make more thiamine and binding of TPP to riboswitch blocks Shine-Dalgarno sequence Weaver, p. 198, Chapter 7 39 (ii) TRANSLATIONAL CONTROL: access to initiation sequences • thiM gene encodes an enzyme required for thiaminesynthesis • 5´ end of thiM mRNA contains a riboswitch whose aptamer binds thiamine pyrophosphate (TPP) • when TPP levels are high, the cell doesn’t want to make more thiamine and binding of TPP to riboswitch blocks Shine-Dalgarno sequence 40 (iii) ANTISENSE RNA • Antisense RNA: complementary to mRNA forms dsRNA with target mRNA • Modes of action: – Duplex RNA sequesters site in target and prevents its function – Duplex RNA changes target mRNA conformation in another transcript region thereby indirectly affecting function – eg. (a) prevent ribosome binding (b) targeting bound mRNA for degradation (c) cause premature transcriptional termination by mimicking terminator Lewin Genes VII 2000 Oxford University Press 41 EnvZ OSMOLARITY REGULATION: TRANSLATIONAL INHIBITION TRANSLATIONAL • EnvZ • • ompF (outer memb protein F) translation controlled by envZ envZ osmoregulation: envZ osmosensor envZ activates ompR in response to high ompR osmolarity osmolarity ompR activator induces micF 174 micF base transcript - an antisense...
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