THE PROLIFERATION POTENTIAL PROTEIN-RELATED (P2P-R) GENE WITH DOMAINSENCODING HETEROGENEOUS NUCLEAR RIBONUCLEOPROTEIN ASSOCIATION AND RB1 BINDING SHOWS REPRESSED EXPRESSION DURING TERMINAL DIFFERENTIATION

Terminal differentiation is associated with repression in the expressi on of the proliferation potential proteins (P2P) subset of heterogeneo us nuclear ribonucleoprotein (hnRNP) proteins. We report here the clon ing and characterization of a 5173-bp P2P-related (P2P-R) cDNA that co ntains a 4214-bp open reading frame. Probes to this cDNA detect a sing le 8-kb mRNA in multiple murine tissues and in proliferating 3T3T cell s, but not in terminally differentiated 3T3T adipocytes. Evidence that this cDNA can encode peptides with domains for hnRNP association was established by showing that such peptides are recognized by two monocl onal antibodies known to detect core hnRNP proteins, and by showing th at the C130 monoclonal antibody, produced against a cDNA-derived fusio n protein, also selectively detects native P2P hnRNP proteins. In addi tion, P2P-R cDNA-derived fusion proteins bind single-stranded nucleic acids, and a P2P-R cDNA-derived antisense oligonucleotide selectively represses P2P expression. Because terminal differentiation is associat ed with modulation in Rb1 function, we assayed if products of this cDN A might interact with Rb1. Evidence that the P2P-R cDNA encodes a prot ein domain that binds Rbl was established using a glutathione S-transf erase fusion protein to selectively precipitate Rbl from cellular extr acts. Data also show that this binding is reduced by competition with the adenovirus E1a protein, indicating that binding occurs through the ''pocket'' domain of Rb1. These results establish that the P2P-R cDNA encodes protein domains involved in both hnRNP association and Rb1 bi nding and complement recent reports that localize Rb1 to sites of RNA processing in the nucleus.