The specific activity of the histones of the Walker, Jensen, and Ehrlich ascites tumors was greater than that of the histones of each of the nontumor tissues studied following incubation of slices or cell suspensions with l-arginine-U-C14 for intervals up to 60 minutes.

In all nontumor tissues studied, the specific activity of the histones was lower than that of proteins of the whole homogenate following 60 minutes of incubation. In the three tumors the specific activity of the histones was equal to or greater than that of the whole homogenate and was generally equal to or greater than specific activities of most of the cytoplasmic proteins.

The uptake of radioactivity into the cytoplasmic proteins of the spleen and mouse pancreas approximated that of the cytoplasmic proteins of the tumors studied.

The results of these experiments fortify the conclusion that an important activity of the neoplastic cell is the biosynthesis of histones and other nuclear proteins.

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Supported by grants from the Jane Coffin Childs Fund and the American Cancer Society.

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