Skip to main content
Biology LibreTexts

7.S: Mutation and Repair of DNA (Summary)

Summary: Causes of Transitions and Transversions

Table 7.1 lists several causes of mutations in DNA, including mutagens as well as mutator strains in bacteria. Note that some of these mutations lead to mispairing (substitutions), others lead to distortions of the helix, and some lead to both. Transitions can be generated both by damage to the DNA and by misincorporation during replication. Transversions occur primarily by misincorporation during replication. The frequency of such errors is greatly increased in mutator strains, e.g. lacking a proofreading function in the replicative DNA polymerase. Also, after a bacterial cell has sustained sufficient damage to induce the SOS response, the DNA polymerase shifts into a an error-prone mode of replication. This can also be a source of mutant alleles.


 

Table. 7.1.  Summary of effects of various agents that alter DNA sequences (mutagens and mutator genes)
Agent (mutagen, etc.)

 

Example                    

 

Result                                      

 

Nucleotide analogs

 

BrdUTP

 

transitions, e.g. A:T to G:C

 

Oxidizing agents

 

nitrous acid

 

transitions, e.g. C:G to T:A

 

Alkylating agents

 

nitrosoguanidine

 

transitions, e.g. G:C to A:T

 

Frameshift mutagens

 

Benz(a)pyrene

 

deletions (short)

 

Ionizing radiation

 

X-rays, g-rays

 

breaks and deletions (large)

 

UV

 

UV, 260 nm

 

Y-dimers, block replication

 

 

 

 

 

 

 

Misincorporation:

 

 

 

 

 

   Altered DNA Pol III

 

mutD=dnaQ; e subunit of DNA PolIII

 

transitions, transversions and frameshifts in mutant strains

 

   Error-prone repair

 

Need UmuC, UmuD, DNA PolIII

 

transitions and transversions in wild-type during SOS

 

   Other mutator genes

 

mutM, mutT, mutY

 

transversions in the mutant strains

 

Additional Readings

  • Friedberg, E. C., Walker, G. C., and Siede, W. (1995) DNA repair and mutagenesis, ASM Press, Washington, D.C.
  • Kornberg, A. and Baker, T. (1992) DNA Replication, 2nd Edition, W. H. Freeman and Company, New York.
  • Zakian, V. (1995) ATM-related genes: What do they tell us about functions of the human gene? Cell 82: 685-687.
  • Kolodner, R.  (1996) Biochemistry and genetics of eukaryotic mismatch repair. Genes & Development10:1433-1442.
  • Sutton MD, Smith BT, Godoy VG, Walker GC. (2000) The SOS response: recent insights into umuDC-dependent mutagenesis and DNA damage tolerance.Annu Rev Genet34:479-497.
  • De Laat, W. L., Jaspers, N. C. J. and Hoeijmakers, J. H. J. (1999) Molecular mechanism of nucleotide excision repair. Genes & Development13: 768-785. This review focuses on nucleotide excision repair in mammals.