consensus sequences: nucleotide sequences that are present in such conserved genetic elements o -10 sequence: TATAAT found in the non-template strand facilitates localized unwinding of DNA o -35 sequence: TTGACA subunit recognizes and binds to this sequence o distance between the subunits is 15> and 20< o Elongation of the chain catalyzed by RNA polymerase core enzyme after the release of the subunit
RNA polymerase contains unwinding and rewinding properties average length of the a transcription bubble is 18 nucleotides pairs ~40 ribonucleotides are incorporated into the growing RNA molecule stability maintained by binding od DNA and the growing RNA chain o Termination of transcription and release of the RNA molecule occurs when RNA polymerase encounters a termination signal complex dissociates to release new RNA molecules two types of terminators rho-dependent terminators: happens only in the presence of rho(p) protein with 2 additional sequences o 50-90 pair sequence upstream from the inverted repeat sequences that produces RNA strand with lots of C’s and fewer G’s therefore, no additional structures specific binding site rut near the 3’ end rho-independent terminators: does not require rho o contain at GC-rich region with inverted repeats followed by 6 or more AT base pairs with A’s present in the template strand o inverted repeat regions produce single-stranded RNA sequences that can base-pair and form hair pin structures immediately after the synthesis this slows the movement of RNA polymerase molecules RNA Polymerases holoenzyme: complete RNA polymerase molecule o composition 2 ’ - involved in the assembly of the tetrameric core ( 2 ’ ) - contains ribonucleotide triphosphate binding site ’ - DNA template binding region sigma ( )- factor - involved only in the initiation of transcription after initiation factor is released Transcription and RNA Processing in Eukaryotes RNA is synthesized in the nucleus & most RNA’s must be transported to the cytoplasm for translation on ribosomes -binding factor
major modifications o 5’-caps are added to the ends of the primary transcripts o 3’-Poly(A) tails are added to the 3’ ends of the transcripts generated by cleavage 20-200 nucleotides long o intron sequences are spliced out 5 RNA polymerases o require the assistance of transcription factors o RNA Polymerase I: located in nucleolus catalyzes the synthesis of all ribosomal RNAs o RNA Polymerase II: transcribes the nuclear genes that encode proteins o RNA Polymerase III: catalyzes the synthesis of the transfer RNA molecules o RNA Polymerase IV: only in plants synthesizes transcripts that are processed into siRNAs o RNA polymerase V: only in plants synthesizes a sunset of siRNAs and non-coding transcripts of genes that are regulated by siRNAs o IV and V important in chromatin remodelling Initiation of RNA Chains all polymerases require protein transcription factors
You've reached the end of your free preview.
Want to read all 15 pages?
- Fall '13
- DNA, nucleosomes assembly