The mammalian cell entry protein 3E (Mce3E), which is encoded by the mce3 operon, is secreted by phagocytosed M. tuberculosis and is expressed during infection in humans.32, 33 MceE3 was recently shown to interfere with the ERK1/2 MAPK signaling pathway by entering the cytosol and localizing to the endoplasmic reticulum (ER).33 Here, it interacts with ERK1/2, tethering it to ER. This evidence concerns the gene MAPK3 and infection.