Binding of a 23 kD endonuclease to the rat liver nuclear matrix

In a previous paper we have described a 23 kD nuclear endonuclease (p23) that was mostly found to exist in a state of association with the isolated rat hepatocyte nuclear matrix. To investigate the nature of this interaction, the nuclear matrix was prepared using different procedures and examined for the presence/absence of the enzyme by activity gel analysis. Treatment of isolated nuclei with sodium tetrathionate (NaTT), a sulfhydryl-cross-linking agent, led to the complete recovery of p23 in the nuclear matrix, whereas incubation of nuclei with dithiothreitol (DTT), a sulfhydryl-reducing agent, led to its complete solubilization and resulting absence from the nuclear matrix. Exposure of the isolated nuclear matrix to DTT in high-ionic strength buffer, a procedure that promotes the solubilization of the internal nuclear matrix, caused the nearly complete solubilization of p23. It was concluded that disulfide bonds play an essential role in the association of p23 with the nuclear matrix and that p23 is mostly localized in the nuclear matrix interior.