Table 1.
Fraction of singletons (Q) for various subsets of protein-encoding E. coli genes
| Source | Protein subset | Number of proteins | Number of singletons | Q |
| SwissProt | Monomers | 137 | 87 | 0.6350 |
| Homo-oligomers + monomers | 596 | 333 | 0.5587 | |
| Hetero-oligomers | 407 | 228 | 0.5602 | |
| Mid-to-large complexes (homotrimer and above) | 334 | 197 | 0.5898 | |
| 1 external interaction | 641 | 342 | 0.5335 | |
| >1 external interaction | 125 | 75 | 0.5000 | |
| Arifuzzaman et al. 2006 [9] | 1 external interaction | 371 | 193 | 0.5202 |
| >1 external interaction | 1,916 | 1,049 | 0.5475 | |
| Ragan 2001 [11] | LGT due to atypical nucleotide composition | 568 | 339 | 0.5968 |
| Beiko et al. 2005 [13] | LGT by Bayesian phylogenetic analysis | 987 | 607 | 0.6150 |
| PEC database | Essential genes | 233 | 173 | 0.7425 |
| E. coli average | 4,308 | 2,382 | 0.5529 |