Nucleic Acids Research

Euplotes eurystomus la a hypotrichous dilate containing a transcrlptionally active nacronucleus (MAC) and a transcrlptlonally Inactive nicronucleus. Soluble MAC chromatin contains a normal complement of Inner his tones, an Hl-like protein which Is very sensitive to proteolysls, and a considerable proportion of non-histone proteins. A combination of N-Tosyl lyslne chloromethyl Ice tone (TLCK) and FMSF was found to be most effective In preventing proteolysis. Mlcroccocal nuclease digestion yielded an average nucleosome repeat length of 187 ± 25 bp for soluble chroaatin; and 190 ± 9 bp for Isolated nacronuclei. Thermal denaturatlon profiles of MAC chromatin in 0.25 mM EDTA display two main transitions at about 76 and 83°C, resembling the melting of soluble chicken erythrocyte chromatin. Circular dichroic spectra of MAC chromatin were compared to soluble chicken erythrocyte chromatin under the same ionic strength conditions and were found to be very similar. 2D chromatln/DNA agarose gel electrophoresis resulted in a diagonal line of DNA staining, which establishes a strict correlation between DNA and chromatin electrophoretic mobility.