title: Mutational analysis of DNA sequences affecting the replication of defective polyomavirus variant D-50.
abstract: The genome of the defective polyomavirus variant D-50 consists of tandemly repeated DNA segments. The repeat unit corresponds to a 17% fragment of polyomavirus DNA (Griffin and Fried (1975) Nature 256, pp. 175-179). To allow mutational analysis, a monomer unit of D-50 DNA was cloned. After excision from the plasmid and ligation to form a random mixture of products, circular head to tail oligomers of the cloned segment were replicated in transfected cells. Those molecules had the same replication properties as original D-50 DNA. Deletion of base sequences assumed to be at the origin of DNA synthesis inhibited the replication completely, whereas a deletion of a segment at the junction of the tandem repeats had only a slight inhibitory effect. Mutation of potential coding sequences of the variant genome had a slight stimulatory effect on DNA synthesis, ruling out that D-50 expresses any protein that stimulates replication. In an attempt to construct variants similar to D-50, cells were transfected with polyomavirus DNA fragments including the sequences of the D-50 monomer unit. However, all these molecules replicated very slowly, suggesting the presence of an element that inhibited DNA synthesis. The combined data show that D-50 genomes can be reconstituted by ligation of monomer units and that the origin of DNA replication was the only essential element of the variant genome, whereas other elements had cis-acting auxiliary functions.
mesh_terms: D001483:Base Sequence; D004261:DNA Replication; D004279:DNA, Viral / Q000032:analysis* / Q000096:biosynthesis; D004587:Electrophoresis, Agar Gel; D005814:Genes, Viral; D009154:Mutation; D010957:Plasmids; D011120:Polyomavirus / Q000235:genetics* / Q000502:physiology; D012091:Repetitive Sequences, Nucleic Acid; D014779:Virus Replication
chemical_list: D004279:DNA, Viral