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VALGUSÜNTEESI INITSIATSIOON EUBAKTERITES

VALGUSÜNTEESI INITSIATSIOON EUBAKTERITES. INITSIATSIOON. 30S subühik mRNA Initsiator-tRNA fMet-tRNA fMet Initiation factor 2 + GTP Initiation factor 1 Initiation factor 3 50S subühik. 30S subühik. Seonduma mRNAga Vahendada initsiatoorset tRNA seondumist mRNAga

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VALGUSÜNTEESI INITSIATSIOON EUBAKTERITES

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  1. VALGUSÜNTEESI INITSIATSIOON EUBAKTERITES

  2. INITSIATSIOON • 30S subühik • mRNA • Initsiator-tRNA fMet-tRNAfMet • Initiation factor 2 + GTP • Initiation factor 1 • Initiation factor 3 • 50S subühik

  3. 30S subühik • Seonduma mRNAga • Vahendada initsiatoorset tRNA seondumist mRNAga • Vahendada 50S seondumist

  4. PEA KAEL PLATVORM KEHA

  5. anti Shine-Dalgarno PEA KAEL PLATVORM KEHA

  6. mRNA • Codes for right positioning of protein synthesis start site into 30S

  7. mRNA AUG 90% GUG 8% UUG 1% AUU 0.1% aSD: AUUCCUCCACU UAAGGAGGUGA A/U rikas SPACING DB START CODON 5’ 3’ ENHANCER SD 6-8 nt SECONDARY STRUCTURE

  8. 30S mRNA

  9. fMet-tRNAfMet • Initiate protein synthesis • Binds to mRNA start codon in P-site on the ribosome

  10. fMet-tRNAfMet • Mismatch at the end of acceptor stem • Three conserved G:C base pairs in the anticodon stem • Formylmethionine

  11. fMet-tRNAfMet • Methionyl-tRNAfMet formyl transferase • Addition of the formyl group to the Met-NH2 creates a block resembling a peptidyl group

  12. fMet-tRNAfMet

  13. INITIATION FACTOR 2 GTP • Stimulation of fMet-tRNAfMet binding to the P site of the ribosome • IF2 favors the association of bacterial ribosomal subunits • Ensures that the initiation complex is formed with only initiator tRNA

  14. INITIATION FACTOR 2 GTP • G domain binds GTP or GDP • C-terminal domain contains all molecular determinants necessary and sufficient for the recognition and binding of fMet-tRNAfMet • IF2 in the GTP form stabilizes the binding of initiator tRNA to the 30S subunit.

  15. INITIATION FACTOR 1 • IF1 prevents premature binding of aminoacyl tRNA • IF1 stimulates IF-2 dependent fMet-tRNAfMet binding to 30S • IF1 modulates the interaction of IF2 with the 30S ribosomal subunit.

  16. INITIATION FACTOR 1 • The smallest IF • IF1 sterically blocks tRNA binding to the A site • IF1 causes movements of of the domains of the 30S with respect to each other, exponate aSD sequence

  17. INITATION FACTOR 3 • IF3 antagonizes the association of 30S and 50S subunits • Accelerates codon-anticodon interaction • Promotes translation of natural mRNA • Promotes dissociation of pseudo-initiation complexes • Promotes binding of other IF • Antagonizes mRNA with weak TIR (IF3-AUU start codon)

  18. INITATION FACTOR 3 • Consists of 192 residues • Can adopt a large variety of conformations • IF3 binding is not affected by the other two factors

  19. INITIATION FACTORS

  20. TRANSLATION INITIATION

  21. TRANSLATION INITIATION

  22. TRANSLATION INITIATION CONTROLL

  23. TRANSLATION INITIATION CONTROLL TRANSLATIONAL COUPLING • L11 - L1 cacggggagcctctcagaggcgttattacccaacttgaggaatttataatg.......gatgactcgctccatcgaaggtactgcacgttccatgggcctggtagtggaggactaagaaatg • L14 – L24 – L5 –... tatggggatttttaacgacctgattttcgggtctcagtagtagttgacattagcggagcactaaaatg...tagtgagaagttcatgcaaattatctctctggcaccagaagtactctaaggagcgaatcatg... aaaaagtccgtttcttcaagtctaacagcgaaactatcaagtaa ttggagtagtacgatg...

  24. TRANSLATION INITIATION CONTROLL • When synthesized in excess over rRNAs, primary rRNA-binding proteins interact with their mRNA and inhibit translation of their own genes and the other genes in their operon. The similarities observed between mRNA and rRNA targets for a number of E.coli ribosomal proteins, sustain the mechanism based on mimicry and competition.

  25. TRANSLATION INITIATION CONTROLL

  26. TRANSLATION INITIATION CONTROLL

  27. TRANSLATION INITIATION

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