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Unformatted text preview: rosophila and mammals contain families of at least seven caspases, classified as either initiator
or effector caspases, that function in a cascade to bring about the events of
apoptosis. All caspases are synthesized as inactive precursors that can be
converted to the active form by proteolytic cleavage, catalyzed by other caspases. Initiator caspases are activated directly in response to the various signals that induce apoptosis, as discussed later in this chapter. The initiator
caspases then cleave and activate the effector caspases, which are responsible for digesting the cellular target proteins that mediate the events of apoptosis (see Figure 17.4). The activation of an initiator caspase therefore starts
off a chain reaction of caspase activation leading to death of the cell.
Genetic analysis in C. elegans initially suggested that Ced-4 functioned as
an activator of the caspase Ced-3. Subsequent studies have shown that Ced4 and its mammalian homolog (Apaf-1) bind to caspases and promote their
activation. In mammalian cells,...
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