P1254413619RuKbk

1
Rolling circle replication
Single-stranded DNA phage fX174
2
l Phage replication
First few replications using q mode, which is
followed by rolling circle replication
3
Which of the following statements is true?

1. DNA replication is always bidirectional
2. DNA replication only needs DNA primers to
   initiate replication
3. Okazaki fragments are DNA/RNA hybrids
4. DNA polymerase, RNA polymerase, templates and
   nucleotides are both necessary and sufficient to
   initiate DNA replication in vivo
5. None of above

C
4
Enzymology of DNA replication
DNA strand separation Helicases unwind double
strand DNA at the expense of ATP Bacterial DnaB
protein Activity can be stimulated by DnaG and
SSBs Single-strand DNA binding proteins (SSBs)
participate in DNA strand separation but do not
catalyze the strand separation process. They bind
to single strand DNA as soon as it forms and coat
it so that it cannot anneal to reform a double
helix. Topoisomerases introduce transient
single or double stranded breaks into DNA and
thereby allow it to change its form, or topology.
5
DNA polymerases

• Three DNA polymerases (I, II, III)
• DNA polymerase I (102 KD) has three different
  enzymatic activities
• DNA polymerase
• 3-5 exonuclease activity
• 5-3 exonulcease activity

(proof reading to increase fidelity)
(remove RNA primers or damage DNA on its path)
6
DNA polymerase III is important for DNA
replication in bacteria
Mutants with a defect in the polA gene (encoding
polymerase I) are viable, suggesting that pol I
is not a major DNA replicating enzyme Mutants
with a defect in the DnaE gene (encoding
polymerase III) are lethal, suggesting that pol
III is the DNA replicating enzyme in
bacteria. Pol II is also dispensable for DNA
replication.
7
March 16-21
Dr. Ravinder Singh will teach three lectures on
RNA splicing for Dr. Lykke-Andersen
Good luck with the rest of your class!