The organization and repair of DNA in the mammalian chromosome. III. Determination of the molecular weight of a mammalian native DNA

Abstract

Abstract The necessary conditions for a unique solution of the sedimentation vs DNA molecular weight equations are considered and applied to the native DNA of the L5178Y mouse leukemia cell. A brief review and critique of the literature of sedimentation anomalies is given to demonstrate that such anomalies are not present in the data reported here. It is shown that the chromosomal DNA of L5178Y cells comes in uniform packages of 1.0 (0.5–2.0) × 10 10 daltons. All pieces are of an identical size which corresponds to the DNA content of about 1/13 the average chromatid. Both the size estimate and the number of such molecules/cell are confirmed by viscoelastometry. This DNA is shown to be free of radioactively demonstrable protein and/or lipid contaminants and of the same isopycnic density as T 4 DNA. Variance analysis is applied to determine the precision of all measurements and to pinpoint major sources of error. A relationship between [η] and M is derived for native DNA in 1.0 M NaCl. A necessary conclusion from these data is that mammalian chromosome models requiring degrees of polynemy greater than 16‐neme (in G 1 ) are incorrect (to the extent that the L5178Y cell is typical of mammalian cells).