Growth Control by the Retinoblastoma Gene Family

The Retinoblastoma family consists of three genes, RB, p107 , and Rb2/p130 , all fundamental in the control of important cellular phenomena, such as cell cycle, differentiation, and apoptosis. The “founder” and the most investigated gene of the family is RB , which is considered the prototype for the tumor suppressor genes (1 ,2 ). The other two genes, p107 and Rb2/p130 , and the proteins they code for, p107 and pRb2/p130, respectively, clearly reflect a high degree of structural and functional similarity to the RB gene product, pRb (3 ,4 ). The RB family proteins were disclosed initially by investigators working on viral oncoproteins. In particular, a set of proteins associated with the Adenovirus 5 E1A oncoprotein was identified, and the bands representing the most abundant ones were named p60, p105, p107, p130, and p300, in keeping with their apparent molecular mass, as determined by SDS-PAGE (5 ). The subsequent characterization of these proteins identified p105 as the product of the RB gene (6 ). Later, genes encoding p107 (7 ,8 ) and pRb2/p130 (9 –11 ) were cloned using different strategies.