The Rb2/p130 gene product is a nuclear protein whose phosphorylation is cycle regulated

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Abstract
The Rb2/p130 protein has been shown to have a high sequence homology with the retinoblastoma gene product (pRb), one of the most well‐characterized tumor suppressor genes, and with pRb‐related p107, especially in their conserved pocket domains, which display a primary role in the function of these proteins. In this study, we report on the biochemical and immunocytochemical characterization of the Rb2/p130 protein, using a polyclonal antibody developed against its “spacer” region included in the pocket domain of the whole protein. We show that pRb/p130 is a phosphoprotein located at the nuclear level and that its phosphorylation pathway can be dramatically reduced by phosphatase treatment. Moreover pRb/p130, with p107, with p107, is one of the major targets of the E1A viral oncoprotein‐associated kinase activity, showing a phosphorylation pattern which is modulated during the cell cycle, reaching a peak of activation at the onset of S‐phase.