Protein ubiquitination is critical for regulation of numerous eukaryotic 
cellular processes such as protein homeostasis, cell cycle progression, immune 
response, DNA repair, and vesicular trafficking. Ubiquitination often leads to 
the alteration of protein stability, subcellular localization, or interaction 
with other proteins. Given the importance of ubiquitination in the regulation of 
host immunity, it is not surprising that many infectious agents have evolved 
strategies to interfere with the ubiquitination network with sophisticated 
mechanisms such as functional mimicry. The facultative intracellular pathogen 
Legionella pneumophila is the causative agent of Legionnaires' disease. L. 
pneumophila is phagocytosed by macrophages and is able to replicate within a 
niche called Legionella-containing vacuole (LCV). The biogenesis of LCV is 
dependent upon the Dot/Icm type IV secretion system which delivers more than 330 
effector proteins into host cytosol. The optimal intracellular replication of L. 
pneumophila requires the host ubiquitin-proteasome system. Furthermore, 
membranes of the bacterial phagosome are enriched with ubiquitinated proteins in 
a way that requires its Dot/Icm type IV secretion system, suggesting the 
involvement of effectors in the manipulation of the host ubiquitination 
machinery. Here we summarize recent advances in our understanding of mechanisms 
exploited by L. pneumophila effector proteins to hijack the host ubiquitination 
pathway.