Several straightforward RNAi screens have been conducted to identify genes that are required for phagocytosis of various species of bacteria by S2 cells. For these experiments, ingestion of bacteria expressing green fluorescent protein (GFP) is monitored and host genes involved in phagocytosis are revealed on the basis of the identity of specific RNAi molecules that inhibit uptake of fluorescence. These screens have revealed that distinct sets of host genes are essential during infection by various pathogens. For example, different pathogens are recognized by distinct cell surface receptors, such as peptidoglycan recognition proteins (PGRPs) (Ramet et al., 2002) , SR-C1 (Ramet et al., 2001) , Eater (Kocks et al., 2005) , Nimrod (Kurucz et al., 2007) or DSCAM (Watson et al., 2005) . However, these screens also defined a core set of intracellular uptake components that are regulated in all types of bacterial infection tested: these included genes required for actin remodeling (e.g. genes encoding proteins of the Arp2/3 complex) and endocytosis (e.g. COPI and COPII), as well as genes encoding factors that are required to recycle endosomes to the cell surface, such as proteins in the exocyst complex (Agaisse et al., 2005; Cheng et al., 2005; Philips et al., 2005; Ramet et al., 2002; Stroschein-Stevenson et al., 2006; Stuart et al., 2007) .