The group I and group II introns have the remarkable ability to excise themselves from an RNA. This is called auto-splicing, or self-splicing. 

Group I introns are more common than group II introns.

TLS Online TPP Program

#Id: 6470

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 6471

#Unit 3. Fundamental Processes

The RNA polymerase I promoter consists of a core promoter and an upstream promoter element (UPE).

TLS Online TPP Program

#Id: 6472

#Unit 3. Fundamental Processes

RNA polymerase I requires two ancillary transcription factors to recognize the promoter sequence. The factor that binds to the core promoter is SL1 which consists of four protein subunits. SL1 has primary responsibility for RNA polymerase recruitment

TLS Online TPP Program

#Id: 6473

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 6474

#Unit 3. Fundamental Processes

The promoters for Classes I and II, 5S and tRNA genes, are internal; they lie downstream of the start point.

TLS Online TPP Program

#Id: 6475

#Unit 3. Fundamental Processes

RNA Polymerase III promoters are bipartite

The exception is in yeast, where the TATA box is more typically found at -90.