Sequence organization in the genomic DNA of the chum salmon, Oncorhynchus keta

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Abstract
The reassociation kinetics and sequence organization of the DNA of chum salmon, O. keta, were measured. Reassociation kinetic studies were carried out by hydroxyapatite chromatography with DNA sheared to lengths of 0.3 and 3.2 kilobases (kb). Kinetic analysis, using a least squares fitting procedure, demonstrated the presence of repeated sequences. Approximately 70% of the DNA sheared to a fragment length of 0.3 kg contained repeated sequences that were reiterated over a range of 30-3000 times. A highly repeated or fold-back component comprised 10% of the DNA at this fragment length. The interspersion of repeated sequences with single copy DNA was indicated by the accelerated rate of reaction of 3.2 kb fragments and the reduced hyperchromicity of such fragments reacted to low values of product of concentration and time of incubation of such fragments reacted to low values of product of concentration and time of incubation (Cot). Digestion with a single strand-specific nuclease demonstrated the presence of 2 fragment lengths of repeated sequences; the 1st, 0.35 kb in length, had a 13.degree. C depression in melting temperature whereas the longer repeat sequences (.gtoreq. 2.0 kb) had a near native melting temperature.
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