Profilin can bind proteins with sequences rich in proline residues at the same time it is bound to actin.

TLS Online TPP Program

#Id: 6024

#Unit 3. Fundamental Processes

DNA polymerase a is unusual because it has the ability to initiate a new strand. It is used to initiate both the leading and lagging strands. 

The enzyme exists as a complex consisting of a 180-kD catalytic (DNA polymerase) subunit, which is associated with three other subunits: the B subunit that appears necessary for assembly, and two small subunits that provide the primase (RNA polymerase) activity.  It has dual capacity to prime and extend chains, this complex is often called pol a/primase.

TLS Online TPP Program

#Id: 6025

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 6026

#Unit 3. Fundamental Processes

Pol a/primase enzyme binds to the initiation complex at the origin and synthesizes a short strand consisting of 10 bases of RNA followed by 20 to 30 bases of DNA called as iDNA. 

It is then replaced by an enzyme that will extend the chain.  On the leading strand, this is DNA polymerase E; on the lagging strand this is DNA polymerase d. This event is called the polymerase switch.

TLS Online TPP Program

#Id: 6027

#Unit 3. Fundamental Processes

DNA polymerase E is a highly processive enzyme that continuously synthesizes the leading strand. Its processivity results from its interaction with RFC clamp loader and trimeric PCNA processivity clamp

TLS Online TPP Program

#Id: 6028

#Unit 3. Fundamental Processes

RFC is a clamp loader that catalyzes the loading of PCNA onto DNA. It binds to the 3’ end of the DNA and uses ATP hydrolysis to open the ring of PCNA so that it can encircle the DNA.

TLS Online TPP Program

#Id: 6029

#Unit 3. Fundamental Processes

The crystal structure of PCNA closely resembles the E. coli b subunit: A trimer forms a ring that surrounds the DNA.  The sequence and subunit organization are different from the dimeric b2 clamp; however, the function is likely to be similar.