A bacteriophage peptide library containing a random ! 5-amino-acid insert was screened for identification of peptide sequence(s) that bind pp60 c-'~. Sequencing the random insert from more than 100 virions indicated that more than 60% of the phage virions that bound to this enzyme contained a GXXG sequence motif in which X was frequently a hydrophobic residue. The GXXG sequence was often repeated as GXXGXXG. Two nonameric peptides were synthesized to determine whether or not the peptide inhibits pp60 ~ ""~ tyrosine kinase activity and the importance of the glycine residues within this sequence. The peptide containing glycine had a Ki of 24 p_M, whereas replacing the glycines with proline increased the Ki value to 3

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Murine p202 is an interferon-inducible primarily nuclear phosphoprotein (52 kDa) whose expression in transfected cells inhibits colony formation. p202-binding proteins include the pocket proteins (pRb, p107 and p130), a p53-binding protein (sm53BP1), and transcription factors (e.g. NF-U UB (p50 and p65), AP-1 (c-Fos and c-Jun), E2F-1, E2F-4, MyoD, and myogenin). p202 modulates the transcriptional activity of these factors in transfected cells. Here we demonstrate that p202 self-associates directly and a sequence in p202, which is conserved among the members of the 200-family proteins, was sufficient for selfassociation in vitro. Our observations reported herein raise the possibility that self-association of p202 may provide a mechanism for the regulation of its activity.z 1998 Federation of European Biochemical Societies.

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