Index >>Viruses and Cancer >>Replication of DNA

Replication of DNA - The DNA replication mechanism can be divided into four stages, initiation, elongation, segregation and maturation.
1.Initiation of replication occurs at a unique site called the origin of replication (O), on the DNA molecule in both polyoma and SV40 viruses.
In SV40 the origin of replication lies at about 0.67 map units on the physical map and in polyoma at about 71 units.
Each round of viral replication requires protein synthesis.
For SV40, initiation requires the A gene product, which is a globular protein.
The nucleotide sequences from the Origin show symmetrical, repeated sequences that are rich in adenine and thymine

3. Segregation of progeny DNA: Chain elongation continues until the two replication forks reach the termination region.
Termination occurs at about 180° from the origin point and does not appear to be dependent on any particular nucleotide sequence.
Separation of the two interlocking DNA duplexes takes place at the termination site.
Each duplex contains a circular parental strand and a linear progeny strand.
The two ends of the latter are separated by a gap.
4. Maturation. During maturation DNA polymerase and polynucleotide ligase activity is required to close the gap and join the two ends of linear DNA to produce a complete, circle.
Winding of the DNA strand then takes place, resulting in the super coiled form.
Proteins are probably involved in the winding process. Histones may be attached to the DNA to produce nucleoprotein complexes.