In Science Signaling this week, researchers in Germany report on their loss-of-function RNAi screen which revealed Ras- and Raf-independent MEK-ERK signaling in human epithelial cells during Chlamydia trachmatis infection. Their study also identified 59 host factors that either positively or negatively influenceChlamydia replication; depletion of Ras or Raf in HeLa cells increased the pathogen's growth.