CHARACTERIZATION OF NOVEL NUCLEAR TARGETING AND APOPTOSIS-INDUCING DOMAINS IN FAS ASSOCIATED FACTOR-1

FAS associated factor 1 (FAF1) has been described as aln unusual prote in that binds to the intracellular portion of the apoptosis signal tra nsducing receptor FAS/Apo-1 and potentiates apoptosis in L-cells, By m eans of mRNA differential display we have identified the avian homolog ue (qFAF) as a fibroblast growth factor-inducible gene in pluripotent cells from EO quail embryos during nesoderm induction in vitro. Later during embryonic development, qFAF expression is ubiquitous. We confir m that qFAF is associated with FAS, and show that it is phosphorylated on serine residues and localized to the nucleus. By in vitro mutagene sis we have delimited a novel nuclear targeting domain to a short 35 a mino acid alpha-helical region in the amino-terminal half of the prote in. The nuclear function of qFAF remains unclear. However, a probably dominant negative deletion mutant of qFAF causes apoptosis of transfec ted cells. This function resides in the carboxy-terminal domain of qFA F which shares remarkable sequence homologies with a putative ubiquiti n conjugating enzyme from Caenorhabditis elegans, Our data indicate a complex function for FAF, which may be executed during FAS signalling and/or in the ubiquitination pathway.