Mechanisms of drug actions during the viral life cycle. Mechanisms of drug actions during the viral life cycle. Twelve drug groups ordered by roman numerals are shown at the bottom, and their drug actions that interfere with major stages of the viral life cycle are highlighted by red arrows. Solid black arrows indicate direct biological pathways involving viral replication, and dotted black arrows indicate biological pathways with intermediate pathways inside host cells. Major viral stages are illustrated, including endocytosis, exocytosis, virus entry, reverse transcription, virus integration, viral transcription, viral translation, virus budding/release, virus maturation, and other pathways associated with cellular compartments (Golgi apparatus, mitochondria, endoplasmic reticulum [ER], ribosome, proteasome, polysome, and endosome) (for more details, see references 177, 300, and 466). Notably, replication pathways of DNA viruses (HCMV, HBV, HPV, HSV, and VZV), RNA viruses (HCV, RSV, and influenza virus), and retroviruses (HIV) diverge after entering host cells. The RNA viruses replicate in the cytoplasm, but DNA viruses and retroviruses further intrude into the nucleus for their DNA synthesis. Note that drug group XIII is not displayed because drugs in this group act mainly as immunoregulatory or antimitotic agents, and they do not directly target viral proteins. Shapes and sizes of proteins and cellular components are not to scale. Erik De Clercq, and Guangdi Li Clin. Microbiol. Rev. 2016; doi:10.1128/CMR.00102-15