DLA trabscription Termination

Question 1

Summarize the basic transcription process

Answer 1

1. Initiation -location of the promoter region(target sequence) by transcription initiation complexes

Promoter DNA is then unwound to form ‘transcription bubble’

2. Elongation- RNA polymerase (RNA pol) catalyzes the synthesis of RNA in the 5’ to 3’ direction (reads the template in the 3’ to 5’ direction)
3. Chain termination & release of RNA
   - The end of the gene is marked by a ‘terminator’ sequence. The RNA pol transcribed this sequence which destabilizes the transcriptional complex, ceases RNA polymerase activity and released the RNA transcript

Question 2

Describe termination of transcription and the effect of intrinsic termination sequences in the RNA transcript (prokaryotic)

Answer 2

1. Palindromic regions that form hairpins varying in length from 7 to 20 bps
2. The stem loop structure includes a G-C rich region and is followed by a run of U residues
3. Palindromic sequences are complementary on either strand
4. GC rich palindrome precedes a sequence of 6-7 U residues in RNA
5. Stem & loop structure formed just before oligoU residues
6. OligoU bind to the DNA template (oligoA) is very weak allowing separation of RNA from the template

Question 3

Explain the termination of transcription can involve EXTRINSIC FACTORS such as the Rho protein (prokaryotes)

Answer 3

1. Rho protein attaches to the recognition site on the RNA
2. Rho moves along the RNA following RNA polymerase
3. RNA polymerase pauses at terminator and Rho catches up
4. Rho unwinds (RNA/DNA helicase activity ) the DNA-RNA hybrid and separates the RNA from the RNA polymerase
5. Termination: RNA polymerase, Rho, and RNA are released

Question 4

Explain the termination of mRNA transcription in eukaryotes is linked directly with the process of poly-adenylation

Answer 4

During the final stages of transcription in eukaryotes the mRNA transcript is cleaved at the 3’ end by “cleavage factors”. This separates the mRNA transcript from the RNA/DNA hybrid (the portion of the newly synthesized mRNA that is still hydrogen bonded with the DNA template ) and terminates transcription

The poly-A tail is then added to the 3’ end of the released transcript

Question 5

Summarize the what causes the termination of eukaryotic transcription

Answer 5

Specific proteins bind to the indicated sequences and facilitate termination and Polyadenylation