“…A-and B-domains are the most conserved among the three RB proteins and are involved in common functional characteristics (Paggi et al, 1996;Mulligan and Jacks, 1998), the most relevant one being the ability to control the cell cycle by negative modulation of the transition between the G1 and S phases (Goodrich et al, 1991;Zhu et al, 1993;Claudio et al, 1994;Starostik et al, 1996). To perform this task, these 'pocket proteins' utilize mechanisms mostly related to inactivation of transcription factors (Kouzarides, 1995), such as those of the E2F family (Cao et al, 1992;Helin et al, 1992Helin et al, , 1993Shirodkar et al, 1992;Beijersbergen et al, 1994;Hijmans et al, 1995;Sardet et al, 1995;Hurford et al, 1997), that promote the cell entrance into the S phase (Ewen, 1994;Weinberg, 1995;Paggi et al, 1996;Mulligan and Jacks, 1998). Indeed, in addition to the cell cycle, the RB family proteins regulate a wide spectrum of complex biological phenomena, as differentiation, embryonic development, apoptosis and senescence ( (Riley et al, 1994;Sidle et al, 1996;Herwig and Strauss, 1997;Stiegler et al, 1998;Thomas et al, 2003;Liu et al, 2004;Kapic et al, 2006) and references therein).…”