Mutational analysis of the Caenorhabditis elegans cell-death gene ced-3

Mutations in the gene ced-3, which encodes a protease similar to interleuki n-lp converting enzyme and related proteins termed caspases, prevent progra mmed cell death in the nematode Caenorhabditis elegans. We used site-direct ed mutagenesis to demonstrate that both the presumptive active-site cystein e of the CED-3 protease and the aspartate residues at sites of processing o f the CED-3 proprotein are required for programmed cell death in vivo. We c haracterized die phenotypes caused by and the molecular lesions of 52 ced-3 alleles. These alleles can be ordered in a graded phenotypic series. Of th e 30 amino acid sites altered by ced-3 missense mutations, 29 are conserved with at least one other caspase, suggesting that these residues define sit es important for the functions of all caspases. Animals homozygous for the ced-3(n2452) allele, which is deleted for the region of the ced-3 gene that encodes the protease domain, seemed to be incompletely blocked in programm ed cell death, suggesting that some programmed cell death can occur indepen dently of CED-3 protease activity.