Double-stranded DNA with the size expected of replicons can be released from Chironomus polytene chromosomes |
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Authors: | Ulf Lönn |
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Institution: | (1) Department of Histology, Karolinska Institutet, S-104 01 Stockholm 60, Sweden |
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Abstract: | The effect of the drug 5-fluorodeoxyuridine on DNA synthesis in Chironomus polytene chromosomes was investigated. The DNA was labelled by injection of radioactive precursor into living animals pre-treated with the drug, extracted with a neutral non-denaturing buffer at 25 ° C and then characterized by gel electrophoresis. After a short pulse a heterogeneous double-stranded DNA population is released from the polytene chromosome. These fragments are later joined together to produce a double-stranded DNA with a size ranging between 8–13 × 106 D. The release of both types of fragments from the polytene chromosome is prevented by lysing the cells at 0 ° C instead of at 25 ° C. The larger double-stranded DNA has the size expected of replicons in Chironomus. The results are discussed in relation to the organization of replication in polytene chromosomes. |
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