ABCG2 and infection: Furthermore, several genes encoding hypothetical products of unknown function and ABC-transporter proteins were also up-regulated in D39 following initial interactions and mutants for many of these genes, e.g. sp_0145, sp_1856, sp_1715, sp_1855 (adhB), sp_1538 (PPIase) and ilvB, were identified using a signature-tagged mutagenesis approach as attenuated for infection of a murine model of streptococcal pneumonia [33].