ASPs (apoptosis specific proteins) are a protein family with a molecular weight betwccn 20K and 140K. Expression has been found mainly in apoptotic cells. However, some family members have also been detected in viable cells. It has been confirmed by confocal microscopy that these proteins are predominately located along the actin cytoskeleton vvith particular high concentrations corresponding to a-actinin. A gene encoding the 32K ASP component has been cloned from a human foetal liver expression library. This 32K ASP protein (termed Apg5L; ApgS [autophagy 5. S. cerevisiae]-like, human [h]Apg5; Apg5) is homologues to the product of the yeast Apg5 gene. In yeast. Apg5 is essential for a novel protein conjugation system during autophagy. It is believed that members of the ASP family (i.e. 32K ASP/Apg5L) are involved in a similar conjugation system in mammals. This assumption is based on the observation that polyclonal antibodies raised against ApgSL recognise a set of proteins with co-localise with members of the ASP family detected by immunofluorescence.