To understand the mechanism of the rotterlin anti-chlamydial activity, we monitored the activity of the p38-regulated/activated protein kinase (PRAK), a known target of rotterlin, in HeLa cells with or without chlamydial infection and in the presence or absence of rotterlin by detecting the phosphorylation of host cell HSP27, a known substrate of PRAK (Fig. 1). The gene discussed is MAPKAPK5; the disease is chlamydia trachomatis infectious disease.