Alkaline degradation of mammalian DNA indicates that the molecule exists in the chromosome as an array of structural subunits. The size of the subunit of single-stranded DNA is circa 5 x 10(8) daltons, and it is of sufficient length to contain a number of synthetic units, replicons. The upper size limit of the multicomponent structure is in excess of 10(10) daltons. Mammalian cells of three different origins have been shown to contain the same basic structural DNA components and these components exist throughout the cell cycle. The nature of the links between the subunits is not known.

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Membrane fractions from mature silver beet (Beta vulgaris) deveined leaf and leaf stem homogenates have associated Ca2"-dependent protein kinase. The Ca2"-dependent protein kinase activity is associated with plasma membranes (density 1.14-1.18 grams per cubic centimeter) as determined from copurification on isopycnic centrifugation with plasma membrane markers such as j-glucan synthetase, eosin-5-maleimidelabeling, and specific naphthylphthalamic acid-binding. The Ca2+-dependent protein kinase is not specifically associated with chloroplasts or mitochondria. The membrane-bound Ca2"-dependent protein kinases were solubilized with 0.8% (volume/volume) Nonidet P40. The solubilized enzymes were extensively purified by a protocol involving binding to diethylaminoethyl-cellulose (Whatman DE-52), Ca2"-dependent binding to phenyl-Sepharose CL-4B, gradient elution from diethylaminoethylSephacel (resolving two distinct Ca2-dependent protein kinases), and gel filtration on Ultrogel AcA 44. These two membrane-derived enzymes have similar molecular weights but differ in protein substrate specificity, in K. values for ATP, and in Ca2"-independent activation by unsaturated fatty acids. The membrane-bound enzymes correspond closely in these properties to two Ca2"-dependent protein kinases present in the soluble phase.

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