LectSlides_RNAregulation_1 - mRNA Structure and Small RNA...

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Unformatted text preview: mRNA Structure and Small RNA Control of Gene Expression Gene Expression gene transcription translation protein Outline 1.  mRNA structure – transx. Elongation 2.  small,non-coding RNAs a.  Translation initiation b.  mRNA stability Transx. Termination •  Happens at the end of a gene or operon (i.e. a group of genes that comprise a transx. unit). •  Signals to terminate transcription are coded in the DNA. •  2 mechanisms for termination –  Rho-dependent (requires protein) –  Rho-independent (requires structure in mRNA) Transx. Attenuation •  Premature transx. termination •  Terminate transx. before RNA pol. reaches the coding region of the gene •  Involves long, untranslated regions of the mRNA trp Operon Expression in Bacillus subtilis •  + Trp in growth medium •  - Trp in growth medium attenuation transx. elongation S1 nuclease mapping of transcripts Tryptophan causes premature termination of trp transcription in vivo 1.  absence of tryptophan 2.  presence of tryptophan read-through transcript (RT) attenuation Shimotshu H et al. 1986 J. Bacteriol. 166:461-471 Two Potential Alternative Structures for the 5' Untranslated Leader Region of trp mRNA Shimotshu H et al. 1986 J. Bacteriol. 166:461-471 Evidence for termination and antitermination stem-loop structures trpE-lacZ Shimotshu H et al. 1986 J. Bacteriol. 166:461-471 TRAP and L-Trp cause premature termination of trp transcription Babitzke P & Yanofsky C 1993 PNAS 90:133-137 Model for TRAP control of terminator formation Babitzke P & Yanofsky C 1993 PNAS 90:133-137 FMN causes premature termination of rib Winkler WC et al. 2002 PNAS 99:15908-15913 Riboswitches •  RNA molecule that directly senses a signal in the absence of any additional regulator factor •  RNA that switches between two conformations •  Found in 5’ untranslated regions of mRNA •  Effect transx. elongation, translation initiation, and mRNA stability Small, Noncoding RNAs (ncRNAs) •  •  •  •  40-400 nucleotides Do not encode proteins Do not function as tRNA or rRNA One group function by basepairing with other RNAs. •  Basepairing with mRNA affects translation and mRNA stability Effects of ncRNAs on mRNA Regulation flhA expression by oxyS [FlhA protein] per cell WT ∆oxyS Strain The oxyS gene does NOT code for a protein oxyS promoter no RBS RNA no protein oxyS RNA sequence looks like the antisense of flhA mRNA The oxyS RNA basepairs with the flhA mRNA to prevent Ribosome access ...
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