In human cells, the centromere- specific protein CENP-B is required to initiate modifications of histone H3 (deacetylation of K9 and K14, followed by methylation of K9) that trigger an association with HP1 that leads to the formation of heterochromatin in the region.

TLS Online TPP Program

#Id: 3264

#Unit 3. Fundamental Processes

The oxoG adduct is highly mutagenic because it can base-pair with adenine as well as with cytosine. If it base-pairs with adenine during replication, it gives rise to a G:C to T:A transversion, which is one of the most common mutations found inhuman cancers.

TLS Online TPP Program

#Id: 3266

#Unit 3. Fundamental Processes

The carcinogenic effects of ionizing radiation and oxidizing agents are partly caused by free radicals that convert guanine to oxoG.

TLS Online TPP Program

#Id: 3267

#Unit 3. Fundamental Processes

Bruce Ames of the University of California at Berkeley devised a simple test for the potential carcinogenic effects of chemicals based on their capacity to cause mutations in the bacterium Salmonella typhimurium.

TLS Online TPP Program

#Id: 3268

#Unit 3. Fundamental Processes

The Ames test uses a strain of S. typhimurium that is mutant for the operon responsible for the biosynthesis of the amino acid histidine. For example, the mutant operon might contain a missense or a frameshift mutation in one of the genes for histidine biosynthesis.

TLS Online TPP Program

#Id: 3271

#Unit 3. Fundamental Processes

Chemicals that are found to be mutagenic in the Ames test can then be tested for their potential carcinogenic effects in animals.

TLS Online TPP Program

#Id: 3272

#Unit 3. Fundamental Processes

Mismatch Repair Correction of the rare mismatches left after replication in E. coli improves the overall fidelity of replication by an additional factor of 10^2 to 10^3.