This family represents the N-terminus (approximately 50 residues) of cyclin-dependent kinase inhibitor 2a p19Arf, which seems to be restricted to mammals. This is a tumour-suppressor protein that has been shown to inhibit the growth of human tumour cells lacking functional p53 by inducing a transient G2 arrest and subsequently apoptosis [1].

1: p14ARF induces G2 arrest and apoptosis independently of p53 leading to regression of tumours established in nude mice. Eymin B, Leduc C, Coll JL, Brambilla E, Gazzeri S; Oncogene 2003;22:1822-1835. PMID:12660818