Question

1. What might be the phenotypes of a cell that has a slower than normal rate of:

a. 5' capping

b. polyadenylation

c. splicing

2. What catalytic sctivities are required for a splicing reaction?

3. What if the cell had a mutation in TFIIH that reduced its kinase activity? Assume that all other functions of TFIIH are the same. If/how would that mutation affect each of the following?

a. Binding of RNA polymerase to the promoter

b. The 5' capping activity

c. The cplicing pattern of the final mRNA

d. Transcription termination

Answer 1

1. a. Due to slower than the normal rate of 5' capping the wing development defect in Drosophila is observed.

b. Due to slower than the normal rate of polyadenylation a mild thrombophilia phenotype is observed.

c. Due to slower than the normal rate of splicing mutations and cardiac,skeletal and muscle abnormalities observed in their phenotype.

2. Splicing is editing if nascent precursor mRna to mature messenger RNA.

Splicing is catalayzed by spliceosome. Splicing is initiated with attact at the 5' splice site by adenosine residue near the 3' end of the intron. This produces the 5' exon and lariat intron. 3' exon intermediates the splicing pathway. The 5' exon carries a 3' hydroxyl group which then attacts the 3' splice site in second transesterification giving the ligated exons and lariat introns as products.