title: Nuclear AP4A-binding activity of sea urchin embryos changes in relation to the initiation of S phase.
abstract: The AP4A-binding activity of sea urchin embryos was studied using radioactively labelled diadenosine 5',5"'-P1,P4-tetraphosphate (Ap4A). Among various subcellular components that can bind [3H]AP4A, nuclei alone showed the highly specific Ap4A-binding activity which was not influenced by the presence of AP4A, AP5A and GP4G. The addition of an excess amount of ATP only slightly reduced the binding of [3H]AP4A to the nuclei. It was found that AP4A binds to the residual proteinaceous structure of nuclei which was resistant to the extraction with 2 M NaCl. The nuclear AP4A-binding activity fluctuated cyclically during each cell cycle, with a transient increase at the beginning of S phase followed by an abrupt decrease within 10 min. When the initiation of S phase was blocked, the increase in the AP4A-binding activity was also prevented. It seems that the binding of AP4A to the nuclear structural protein is involved in the initiation of S phase.
mesh_terms: D000227:Adenine Nucleotides / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000302:isolation & purification; D002451:Cell Compartmentation; D002453:Cell Cycle; D002467:Cell Nucleus / Q000378:metabolism; D004261:DNA Replication; D015226:Dinucleoside Phosphates; D006150:Guanine Nucleotides / Q000378:metabolism; D011485:Protein Binding; D012617:Sea Urchins / Q000166:cytology / Q000196:embryology*
chemical_list: D000227:Adenine Nucleotides; D002352:Carrier Proteins; D015226:Dinucleoside Phosphates; D006150:Guanine Nucleotides; C020733:diadenosine tetraphosphate