RNA polymerase ⅱ catalyzes the synthesis of precursor mRNA. Precursor tRNA is produced by RNA polymerase ⅲ and processed into mature tRNA. [Test site] The mechanism of eukaryotic gene transcription. In eukaryotes, the synthesis of precursor rRNA is catalyzed by RNA polymerase ⅰ; The transcription product of RNA polymerase I is 45SrRNA, and various rrnas except 5SrRNA are produced by splicing modification. Eukaryotic rRNA gene is a moderately repetitive gene with hundreds to tens of thousands of copies, while human rRNA gene has about 300 copies.
RNA polymerase ⅱ catalyzes the synthesis of precursor mRNA; Precursor tRNA is produced by RNA polymerase ⅲ and processed into mature tRNA.
Post-transcriptional processing:
There are four types of eukaryotic rRNA: 5S, 5.8S, 18S and 28S. Among them, 5.8S, 18S and 28S genes form a transcription unit (precursor molecule) to produce 45S precursor RNA. Post-transcriptional processing of rRNA involves the binding of precursor rRNA to protein, followed by cleavage and methylation.
The processing of precursor tRNA includes: (2) endonuclease cuts off both ends of tRNA; (2) exonuclease of nucleic acid cuts down additional sequences from the 5' end one by one; (3) adding CCA-OH structure at the 3' end; (4) base modification reaction.
There are several types of modifications of precursor tRNA: (1at the 3' end of precursor trna) U is replaced by CCA; (2) methylation of purine base or ribose C2; (3) The uridine is reduced to dihydrouridine (DH) or the translocation reaction in nucleoside becomes pseudouridine (tψ); (4) Some adenosine deaminations are converted into hypoxanthine nucleotides (AMP→IMP).
The post-transcriptional processing of mRNA includes: (1) capping the 5' end; (2) splicing by adding Polya(3) intron at the 3' end; (4)RNA editing.