Base excision repair (BER) systems directly remove the damaged base and replace it in DNA.

TLS Online TPP Program

#Id: 6789

#Unit 3. Fundamental Processes

The piRNAs which are 24–34 nucleotides long are derived in a manner that does not involve a dsRNA precursor

piRNAs are generated by processing long single-stranded transcripts covering so-called piRNA clusters found in the genome. This processing does not require Dicer.

TLS Online TPP Program

#Id: 6790

#Unit 3. Fundamental Processes

The miRNAs used in RNAi are produced as large RNA primary transcripts called pri-miRNA that are self-complementary and can automatically fold into a double-strand hairpin structure.

TLS Online TPP Program

#Id: 6791

#Unit 3. Fundamental Processes

pri-miRNA is processed in a two-step reaction

The first step is catalyzed by Drosha, an RNase III superfamily member endonuclease, in the nucleus. Drosha reduces the pri-RNA to about a 70-bp, hairpin-shaped precursor fragment, pre-miRNA

TLS Online TPP Program

#Id: 6792

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 6793

#Unit 3. Fundamental Processes

The two cleavages thus generate the 65-nucleotide pre-miRNA composed of the 22 bp (two helical turns) of dsRNA and the top loop.

TLS Online TPP Program

#Id: 6794

#Unit 3. Fundamental Processes