Replication
Following infection of a cell, a cascade of herpes virus proteins, called immediate-early, early, and late, is produced. Research using flow cytometry on another member of the herpes virus family, Kaposis sarcoma-associated herpesvirus, indicates the possibility of an additional lytic stage, delayed-late. These stages of lytic infection, particularly late lytic, are distinct from the latency stage. In the case of HSV-1, no protein products are detected during latency, whereas they are detected during the lytic cycle.The early proteins transcribed are used in the regulation of genetic replication of the virus. On entering the cell, an α-TIF protein joins the viral particle and aids in immediate-early transcription. The virion host shutoff protein (VHS or UL41) is very important to viral replication. This enzyme shuts off protein synthesis in the host, degrades host mRNA, helps in viral replication, and regulates gene expression of viral proteins. The viral genome immediately travels to the nucleus, but the VHS protein remains in the cytoplasm.The late proteins form the capsid and the receptors on the surface of the virus. Packaging of the viral particles — including the genome, core and the capsid - occurs in the nucleus of the cell. Here, concatemers of the viral genome are separated by cleavage and are placed into formed capsids. HSV-1 undergoes a process of primary and secondary envelopment. The primary envelope is acquired by budding into the inner nuclear membrane of the cell. This then fuses with the outer nuclear membrane. The virus acquires its final envelope by budding into cytoplasmic vesicles.
Clinical trials are ongoing to test whether nitisinone can prevent ochronosis experienced by older alkaptonuria patients. History
Nitisinone was discovered as part of a program to develop a class of herbicides called HPPD inhibitors. It is a member of the benzoylcyclohexane-1,3-dione family of herbicides, which are chemically derived from a natural phytotoxin, leptospermone, obtained from the Australian bottlebrush plant (Callistemon citrinus). HPPD is essential in plants and animals for catabolism, or breaking apart, of tyrosine. In plants, preventing this process leads to destruction of chlorophyll and the death of the plant. In toxicology studies of the herbicide, it was discovered that it had activity against HPPD in rats and humans.In Type I tyrosinemia, a different enzyme involved in the breakdown of tyrosine, fumarylacetoacetate hydrolase is mutated and doesnt work, leading to very harmful products building up in the body. Fumarylacetoacetate hydrolase acts on tyrosine after HPPD does, so scientists working on making herbicides in the class of HPPD inhibitors hypothesized that inhibiting HPPD and controlling tyrosine in the diet could treat this disease. A series of small clinical trials attempted with one of their compounds, nitisinone, were conducted and were successful, leading to nitisinone being brought to market as an orphan drug  Swedish Orphan International, which was later acquired by Swedish Orphan Biovitrum (Sobi). In 201, Cycle Pharmaceuticals launched Nityr in the United States through Cycle Vita. Research
Nitisinone is being studied as a treatment for alkaptonuria. References
External links
"Nitisinone". Drug Information Portal. U.S. National Library of Medicine.