In the last decade, much of the research in cell proliferation has been concentrated in the signals that initiate cell growth. Very little is know about the opposite end of the cellular life cycle, particularly cell death. All multicelluar organisms contain genes that can trigger a specific cell's demise. These suicide genes along with the signals and factors that regulate their expression are just beginning to be discovered. Programmed cell death, also called apoptosis, is essential for normal development and tissue homeostasis.
Apoptosis also provides a primitive form of defense against viral infections.
Infected cells accept apoptosis to prevent the propagation of progeny virus thereby slowing down the spread of the infection. Some ingenious viruses have evolved proteins to circumvent this defense mechanism. The baculovirus carries a gene that encodes for a 35,000 Dalton protein. This protein, P35, blocks apoptosis in mammalian, murine, and insect cell lines as well as in developing embryos of the fruit fly Drosophila and the nematode C. elegans . The ability of P35 to block apoptosis in such a diverse range of organisms induced by different signals suggests that it acts at an evolutionary conserved step in the apoptotic pathway.