BIOC 406 Lecture 19 - RNA Processing and Genetic Code

What are the steps of mRNA processing?

1) 5’ cap addition

2) 3’ polyadenylation

3) Splicing to remove introns

What is used in 5’ cap addition?

7-methyguanosine and the capping enzyme

Steps of 5’ cap addition

1) Hydrolysis removes the 5’ gamma phosphate from pre-mRNA

2) Guanylation of pre-mRNA through the tri-phosphate bridge

3) Methylation of guanosine using SAM

When does 5’ cap addition take place?

During elongation by binding to RNAP II

When is the 3’ end polyadenylated?

After termination of the RNA sequence

What enzyme carries out splicing?

The spliceosome, which is made of snRNPs

Steps of the Lariat method

1) the 2’ OH breaks the phosphodiester bond at the GU donor site

2) This forms a loop upstream of the GU, leaving the 3’ OH exposed on the AG acceptor site

3) The 3’ OH then attacks the AG acceptor, kicking off the intron lariat

What are Group 1 introns?

Autocatalytic introns that only use the 3’ OH for energy