Animal Biotechnology

TRANSCRIPTION IN EUKARYOTES

• Three eukaryotic polymerases transcribe different sets of genes.
  • RNA polymerase I (RNA Pol I) is located in the nucleoli. It is responsible for the synthesis of the precursors of most rRNAs. The pre rRNA transcription units contain three sequences that encode the 18S, 5.8 S,28SrRNAs.
  • RNA polymerase II (RNA Pol II) is located in the nucleoplasm and is responsible for the synthesis of mRNA precursors and some small nuclear RNAs. Many RNA polymerase II promoters contain a sequence called TATA box which is situated 25-30bp upstream from the start site of transcription.The pre mRNAs are processesd after synthesis by cap formation at the 5' end of RNA and poly(A) addition at the 3' end, as well as removal of introns by splicing.
  • RNA polymerase III (RNA Pol III) is located in the nucleoplasm. It is responsible for the synthesis of the precursors of 5S rRNA, tRNAs and small nuclear and cytosolic RNAs.
    • Each RNA polymerase has 12 or more subunits.
    • In Eukaryotes , transcription factors have a modular structure consisting of DNA binding and transcription activation domains. Some transcription factors have dimerization domains.