Table 1.
Mean excess of guanines versus cytosines in coronavirus genomes
| Virus genomea |
Extra guanines compared with cytosines per 100 bp of genomic sequenceb |
||
|---|---|---|---|
| Lc | Sc | L-Sc | |
| SARS-CoV | 1.8 | −1.7 | 3.5 |
| BCoV | 7.8 | 3.5 | 4.3 |
| MHV | 7.1 | 3.5 | 3.6 |
| PEDV | 4.4 | 1.4 | 3.0 |
| HCoV | 6.0 | 1.8 | 4.2 |
| IBV | 5.9 | 4.2 | 1.7 |
Abbreviations: BCoV, enteric bovine coronavirus; IBV, avian infectious bronchitis virus; HCoV, human coronavirus (229E); PEDV, porcine epidemic diarrhea virus; SARS-CoV, severe acute respiratory syndrome coronavirus.
These averages represent the trends depicted in Figure 1 but without taking into account G+C content (which ranges from 37% to 42% in Coronaviridae). GC content does not affect the trends observed in Figure 1.
The change in number of guanines compared with cytosines is probably due to cytosine deamination in the minus strand on the short arm and reflects additional mutational pressure on that arm. Notably, this change is comparable with SARS-CoV and other coronaviruses, whereas the guanine excess on the long arm is much smaller. Definitions: L, long arm; S, short arm; L-S, change on short arm.