The human retinoblastoma gene product Rb plays an important role in the negative regulation of cell proliferation. The Rb family includes p107 and p130, which form complexes with E2F proteins, and share a high degree of structural homology in the adenovirus E1A binding domain, which plays a primary role in the function of these proteins. p130 is specifically phosphorylated on serine and threonine residues in cells arrested in G0 by serum deprivation or density arrest, and these residues are clustered within a short co-linear region unique to p130 defined as the Loop.
