Presence of a unique set of nuclear proteins at the sites sensitive to RNase A as well as DNase I.

A unique and simple set of proteins (S1 proteins) has been detected in the cell nuclei of various tissues of the rat (Inoue et al. (1983) Eur. J. Biochem. 135, 61-68). They were liberated from the nuclei by digestion with DNA-hydrolyzing enzymes under the conditions where transcriptionally active chromatin is preferentially digested and released into the reaction supernatant. S1 proteins account for 20% of the total supernatant proteins (Higashi et al. (1984) Biochem. Int. 9, 697-704). The present study demonstrates that S1 proteins occur at the sites sensitive to RNase A as well as DNase I, and are rapidly liberated from the nuclei by digestion with either enzyme.