STRUCTURAL PROTEIN-4.1 IS LOCATED IN MAMMALIAN CENTROSOMES

Structural protein 4.1 was first characterized as an important 80-kDa protein in the mature red cell membrane skeleton. It is now known to b e a member of a family of protein isoforms detected at diverse intrace llular sites in many nucleated mammalian cells. We recently reported t hat protein 4.1 isoforms are present at interphase in nuclear matrix a nd are rearranged during the cell cycle. Here we report that protein 4 .1 epitopes are present in centrosomes of human and murine cells and a re detected by using affinity-purified antibodies specific for 80-kDa red cell 4.1 and for 4.1 peptides. Immunofluorescence, by both convent ional and confocal microscopy, showed that protein 4.1 epitopes locali zed in the pericentriolar region. Protein 4.1 epitopes remained in cen trosomes after extraction of cells with detergent, salt, and DNase. Hi gher resolution electron microscopy of detergent-extracted cell whole mounts shelved centrosomal protein 4.1 epitopes distributed along cent riolar cylinders and on pericentriolar fibers, at least some of which constitute the filamentous network surrounding each centriole. Double- label electron microscopy showed that protein 4.1 epitopes were predom inately localized in regions also occupied by epitopes for centrosome- specific autoimmune serum 5051 but were not found on microtubules. Our results suggest that protein 4.1 is an integral component of centroso me structure, in,which it may play an important role in centrosome fun ction during cell division and organization of cellular architecture.