8.) What is the role of FACT in eukaryotic transcription? 9.) The chicken ovalbumin gene has five introns and interrupting the coding sequences or exons. How many R-loops will be observed if DNA of the gene and cytoplasmic mRNA are mixed under conditions that allow hybridization? How many R-loops will be observed if nuclear pre- mRNA is used? 10.) What is the function of RNA editing? How does it occur? 11.) Compare and contrast Rho dependent and Rho independent termination in prokaryotes. 12.) Describes the characteristics of promoters and enhancers? What is the function of each? Solution 8) FACT, the abbreviated form of Facilitates chromatin transcription, is a heterodimeric protein which helps in the process of elongation in eukaryotic DNA transcription. The chromatin-coated DNA, which is wound along with histone proteins in nucleosomes, are difficult to be transcribed because the RNA Polymerase II cannot access the DNA. FACT binds to the H2A-H2B dimer of histone proteins upstream and removes it from the DNA, allowing RNA PolI to carry out elongation. Behind the RNA Pol II, FACT reassembles the H2A-H2B dimer into nucleosomes. 9) R-loop structure is formed by 3-nucleic acids, wherein a double-stranded DNA is hybridized to an RNA component, leaving behind a looped out single-stranded DNA. In the laboratory, an R-loop can be formed by hybridization of a double-stranded DNA (containing introns) to a mature mRNA. The non-complementary region of each intron will form a single stranded R-loop. Therefore, the chicken ovalbumin gene having 5 introns when hybridized to cytoplasmic mRNA, will produce 5 R-loops. This is because, the mRNA have spliced out the intronic regions. In a pre-mRNA, splicing of introns has not yet taken place. Therefore when a nuclear pre-mRNA is hybridized to the given DNA, no R-loops will be observed. 10) RNA editing is a process by which transcribed mRNA undergo changes in few or more bases throughout the polynucleotide chain. These changes are different from the RNA processing events such as capping, polyadenylation of splicing. In RNA editing, the changes comprise of base insertion, deletion or substitution events and mostly requires a guide RNA (gRNA) to accomplish these editing. 11) In prokaryotes, the termination of transcription occurs by either two ways: Rho-independent or Rho-dependent termination. Rho-dependent termination: The RNA being transcribed forms a hairpin loop structure which causes the RNA polymerase to dissociate and causes termination. This is also known an intrinsic termination. Rho-dependent termination: A protein called Rho-factor, attaches itself at the termination site of RNA. When it encounters the RNA Polymerase, it binds and removes the polymerase from the template, causing termination. 12) Promoters are regions of the DNA located immediately upstream of the transcription start site. These regions are 200 bp or more in length and usually, have few dispersed conserved sequences. Enhancers are reg.

1. 8.) What is the role of FACT in eukaryotic transcription?
9.) The chicken ovalbumin gene has five introns and interrupting the coding sequences or exons.
How many R-loops will be observed if DNA of the gene and cytoplasmic mRNA are mixed
under conditions that allow hybridization? How many R-loops will be observed if nuclear pre-
mRNA is used?
10.) What is the function of RNA editing? How does it occur?
11.) Compare and contrast Rho dependent and Rho independent termination in prokaryotes.
12.) Describes the characteristics of promoters and enhancers? What is the function of each?
Solution
8) FACT, the abbreviated form of Facilitates chromatin transcription, is a heterodimeric protein
which helps in the process of elongation in eukaryotic DNA transcription.
The chromatin-coated DNA, which is wound along with histone proteins in nucleosomes, are
difficult to be transcribed because the RNA Polymerase II cannot access the DNA. FACT binds
to the H2A-H2B dimer of histone proteins upstream and removes it from the DNA, allowing
RNA PolI to carry out elongation. Behind the RNA Pol II, FACT reassembles the H2A-H2B
dimer into nucleosomes.
9) R-loop structure is formed by 3-nucleic acids, wherein a double-stranded DNA is hybridized
to an RNA component, leaving behind a looped out single-stranded DNA.
In the laboratory, an R-loop can be formed by hybridization of a double-stranded DNA
(containing introns) to a mature mRNA. The non-complementary region of each intron will form
a single stranded R-loop. Therefore, the chicken ovalbumin gene having 5 introns when
hybridized to cytoplasmic mRNA, will produce 5 R-loops. This is because, the mRNA have
spliced out the intronic regions.
In a pre-mRNA, splicing of introns has not yet taken place. Therefore when a nuclear pre-mRNA
is hybridized to the given DNA, no R-loops will be observed.
10) RNA editing is a process by which transcribed mRNA undergo changes in few or more bases
throughout the polynucleotide chain. These changes are different from the RNA processing
events such as capping, polyadenylation of splicing. In RNA editing, the changes comprise of
base insertion, deletion or substitution events and mostly requires a guide RNA (gRNA) to
accomplish these editing.
11) In prokaryotes, the termination of transcription occurs by either two ways: Rho-independent
or Rho-dependent termination.
Rho-dependent termination: The RNA being transcribed forms a hairpin loop structure which

2. causes the RNA polymerase to dissociate and causes termination. This is also known an intrinsic
termination.
Rho-dependent termination: A protein called Rho-factor, attaches itself at the termination site of
RNA. When it encounters the RNA Polymerase, it binds and removes the polymerase from the
template, causing termination.
12) Promoters are regions of the DNA located immediately upstream of the transcription start
site. These regions are 200 bp or more in length and usually, have few dispersed conserved
sequences.
Enhancers are regions of the DNA that are located far upstream from the gene and are short in
length (<10bp). These regions contain closely spaced sequences.
Both promoters and enhancers are regions where transcription factors bind and is required for
efficient transcription.