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Table 1 Hypotheses proposed to explain GC content variations in eubacteria

From: On the molecular mechanism of GC content variation among eubacterial genomes

Hypotheses

Time

Content

Reference

UV resistance

1970

Since ultraviolet radiation induces the formation of thyminedimers, higher GC content gives a selective advantage to organisms living in niches that are susceptible to direct and intense sunlight.

16,17

Thermal adaptation

1984

Thermophilic organisms demonstrate a tendency to high GC content because thermostable and thermolabile amino acids are encoded by GC-rich and GC-poor codons respectively.

18, 19

AT to GC mutation

1988

Practically all organisms are subjected to directional mutation pressure and this offers plausible explanations for the intensive GC content heterogeneity among different chromosomal regions of vertebrate genomes.

20

Metabolic resource

1995

Differences in directional nucleotide substitution among lineages of mammals can be explained by changes in metabolic physiology. This relationship is thought to be mediated by the effect of oxygen radicals.

21

Coding sequence length

1996

The longest coding sequences (exons) of vertebrates and genes of prokaryotes are more GC-rich than the shortest ones.

22, 23

Nitrogen-fixation

1998

There is a significantly higher GC content in the nitrogen-fixing members of the genus than in those unable to fix nitrogen.

24

Oxygen requirement

2002

Aerobic prokaryotes display a significant increment in genome GC% in relation to anaerobic ones.

25

Environment pressure

2005

The GC content of complex microbial communities seems to be globally and actively influenced by the environment, such as bacteria in surface water samples having a GC-content median of around 34%, while for soil samples, it is around 61%.

26

Genome size

2006

The relationship between genome size and GC level is valid for aerobic, facultative, and microaerophilic species.

27

DNA polymerase III

2007

According to the dimeric combination of alpha subunits, GC contents of eubacterial genomes are partitioned into three groups with distinct GC content variation spectra: dnaE1 (full-spectrum), dnaE2/dnaE1 (high-GC), and polC/dnaE3 (low-GC).

28