title: MCM4 shares homology to a replication/DNA-binding domain in CTF and is contacted by pRb.
abstract: pRb limits the initiation of DNA replication. By immunoblotting of in vitro kinase assays we show that Cdk4,6-cyclin D contributed to pRb-phosphorylation at Ser-608, which was necessary to release pRb from chromatin in Nalm-6 cells, demonstrated by immunoprecipitations of differential cell extractions. A new binding protein of under-phosphorylated pRb, MCM4, was identified using LexA-Rb(561-660) in the two-hybrid assay. Sequence analysis revealed a novel conserved motif in MCM4's COOH-terminus with homology to the DNA-binding/viral replication activation domain of CTF/NF-I indicating their implication in the same process, and suggesting a model that CTF/NF-I stimulated binding of MCM4 to DNA, thereby to under-phosphorylated pRb. Accordingly, the pRb-MCM4-CTF/NF-I complex was immunodetected in Nalm-6 cells. Moreover, the motif was also in XPD, pointing to a collaboration of CTF/NF-I with XPD in nucleotide excision repair and in basal transcription and with MCM4 in the assembly of MCM complexes in which pRb specifically contacted MCM4.
authors.affiliation: Department of Clinical Research, University of Bern, Switzerland. Nicole.schmitz@dkf3.unibe.ch
authors.forename: Nicole M R
authors.initials: NM
authors.lastname: Schmitz
authors.forename: Kurt
authors.initials: K
authors.lastname: Leibundgut
authors.forename: Andreas
authors.initials: A
authors.lastname: Hirt
mesh_terms: D000595:Amino Acid Sequence; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D064148:Minichromosome Maintenance Complex Component 4; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D010766:Phosphorylation; D016160:Retinoblastoma Protein / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000378:metabolism
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D016160:Retinoblastoma Protein; D012694:Serine; C099243:MCM4 protein, human; D064148:Minichromosome Maintenance Complex Component 4