title: The mechanism of replication of phi X 174. XVIII. Gene A and A* proteins of phi X 174 bind tightly to phi X 174 replicative form DNA.
abstract: Evidence is presented that the gene A and A * proteins of bacteriophage phi X 174 form covalent associations with the 5' ends of the DNA molecules when superhelical phi X replicative form DNA is nicked by a combination of these proteins in vitro. This evidence is: 1, The 5' ends of the DNA molecules nicked by the gene A protein and reacted with bacterial alkaline phosphatase were protected against subsequent phosphorylation by polynucleotide kinase even after treatment of the nicked DNA with SDS and pronase followed by centrifugation on a high-salt neutral sucrose gradient. 2, Iodinated pronase-sensitive material remained attached to the nicked replicative form DNA and could not be removed by exposure to SDS or 2 M NaCl, either by sedimentation through high-salt neutral sucrose gradients, or by CsCl equilibrium centrifugation. 3, Iodinated pronase-sensitive material was detected on DNA that had been nicked during the reaction, but not on unreacted DNA. 4, Electrophoresis of the iodinated pronase-sensitive, DNA-bound material in SDS-polyacrylamide gels after DNAse digestion revealed that it was composed almost entirely polypeptides with electrophoretic mobilities similar to those of the gene A and A * proteins. We speculate that the gene * protein may be essential for normal progeny single-stranded DNA synthesis in vivo.
mesh_terms: D010584:Bacteriophage phi X 174 / Q000502:physiology*; D004261:DNA Replication; D004277:DNA, Single-Stranded / Q000096:biosynthesis; D004278:DNA, Superhelical / Q000378:metabolism; D004279:DNA, Viral / Q000096:biosynthesis*; D004720:Endonucleases / Q000302:isolation & purification / Q000378:metabolism*; D014764:Viral Proteins / Q000302:isolation & purification / Q000378:metabolism*; D014779:Virus Replication
chemical_list: D004277:DNA, Single-Stranded; D004278:DNA, Superhelical; D004279:DNA, Viral; D014764:Viral Proteins; D004720:Endonucleases