Figure 1.

DNase 1 is the major serum nuclease degrading chromatin. (A) Heparin enhances chromatin degradation in serum. Normal serum of a wild type C57BL/6 mouse was incubated in the presence of purified chromatin for 0–4 hours (h) with (right) or without (w/o, left) heparin. Chromatin was then analyzed by 1.5% agarose gel electrophoresis. One representative of five independent experiments is depicted. bp, base pair; M, molecular weight marker (100 bp ladder). (B) Chromatin degradation is impaired in serum from DNase1-deficient mice. Sera from wild type (WT) or DNase1^−/−/Trap1^m/m mice were incubated with chromatin in the presence of heparin for 0–15 h. Chromatin was then analyzed by 1.5% agarose gel electrophoresis. One representative of nine independent experiments is depicted. (C) C1q is not required for optimal chromatin degradation. Sera from wild type (WT), DNase1^−/−/Trap1^m/m (D1^−/–/T1^m/m), C1qa^−/− or DNase1^−/−/Trap1^m/m/C1qa^−/− (D1^−/–/T1^m/m/C1qa^−/–) mice were incubated with chromatin in the presence of heparin for 0–4 h. Chromatin was then analyzed by 1.5% agarose gel electrophoresis. One representative of three independent experiments is depicted (using three independent chromatin preparations). For comparison, purified chromatin (Chrom) not incubated with serum was loaded.