MUTATIONAL EFFECTS ON THE P16(INK4A) TUMOR-SUPPRESSOR PROTEIN

Several point mutations of p16(INK4a) were studied by site-specific mu tagenesis and functional analysis to assess the effects of these mutat ions on the function of the protein, These mutations were reported in several malignancies. Three deletional mutants of p16(INK4a) were also analyzed to reveal the relationship between p16(INK4a) and p15(INK4b) and to test the importance of the ankyrin repeats observed in both pr oteins. We studied the activity of these mutants using the yeast two-h ybrid system and an in vitro kinase assay. Our results suggest that po int mutations in the conserved ankyrin consensus affect the activity o f p16(INK4a). However, not all of the point mutations observed in tumo rs have a detectable effect on the activity. The COOH-terminal region of p16(INK4a) is not required for the protein to bind and to inhibit C DK4, but the deletion of the 4th ankyrin repeat abolished the activity completely.