Table 2.

Codon biases of the nucleotide sequence of the E.coli signal peptides

Sequence data	Frequency of AAA codon at position +2
Whole E.coli K12 genome	440/4241 (10.3%)
Unverified E.coli signal sequences	22/45 (48.9%)
Verified E.coli signal sequences	16/54 (29.6%)

E.coli signal sequence data set were obtained from a signal peptide database (http://proline.bic.nus.edu.sg/spdb/). This database currently contains 99 entries of E.coli signal sequences: 54 of the entries are experimentally verified signal sequences (the N-terminal amino acid residues were sequenced), and 45 are computationally predicted sequences (17).