DNA synthesis in cells deprived of arginine was examined. Three lines of evidence indicated that tritiated thymidine ([3H]TdR) incorporation in arginine-starved cells was due to replicative rather than repair DNA synthesis. (a) When made in the presence of bromodeoxyuridine, the [3H]TdR-labeled DNA sedimented at hybrid density in isopycnic gradients. (b) As determined by the diphenylamine reaction, there was a 15% increase in the chemical amount of DNA per culture 30 h after arginine deprivation. (c) [3H]TdR incorporation was hydroxyurea-sensitive. Alkaline velocity sedimentation of the total DNA made during starvation revealed the existence of two distinct size classes: most of the DNA sedimented at a position analogous to that of control DNA, but 40% migrated one-third the distance of the bulk. After arginine restoration, these shorter pieces appeared to be chased into DNA of normal length; thus, one lesion in deprived cultures may cause an arrest in completion of DNA stretches to mature size. These findings, together with results of morphological studies of starved cells, suggest that changes induced by arginine deficiency effect the organization of nucleoproteins. These changes are reversible upon arginine restoration.

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