E. coli SSB is a tetramer of 74 kD that binds single-stranded DNA cooperatively

TLS Online TPP Program

#Id: 1983

#Unit 3. Fundamental Processes

Capping is done by a dimeric nuclear enzyme which has two subunits and three functions

1. Guanylyl-transferase (GT)

2. Methyltransferase (MT)

TLS Online TPP Program

#Id: 1984

#Unit 3. Fundamental Processes

Structure of cap is

   

TLS Online TPP Program

#Id: 1985

#Unit 3. Fundamental Processes

Binding of the capping enzyme to the TFIIH mediated serine 5–phosphorylated CTD stimulates the activity of the enzyme.

TLS Online TPP Program

#Id: 1986

#Unit 3. Fundamental Processes

RNA polymerases I or III do not have a CTD so no capping is stimulated

TLS Online TPP Program

#Id: 1987

#Unit 3. Fundamental Processes

The 5’ cap of most mRNA is monomethylated, but some small noncoding RNAs are trimethylated.

TLS Online TPP Program

#Id: 1988

#Unit 3. Fundamental Processes

Small ncRNAs involved in RNA splicing in the spliceosome are trimethylated at terminal guanine. This structure is called a trimethylated cap. The enzymes for these additional methyl transfers are present in the cytoplasm.