Negative stain images of Mlh1-Mlh3 binding to circular DNA using a K2 direct detector.

<p>(A) Representative electron micrograph of sample containing 3.6 nM of 2.7 kb circular DNA in the absence of protein. DNA is indicated by black arrow. A total 50 particles were assessed and all were classified as naked DNA particles. The inset area contains a zoomed view of one of the DNA molecules. The image for this molecule is 2-fold magnified with respect to the entire micrograph in this panel. (B) The electron micrograph shows a sample containing 300 nM Mlh1-Mlh3 in the absence of DNA. (C) Representative electron micrograph of sample containing 30 nM Mlh1-Mlh3 + 3.6 nM 2.7 kb circular DNA. Protein and DNA form both loosely (white arrows) and tightly packed (black arrow) clusters. Naked DNA was also observed in this sample but it is not shown in the electron micrograph. A total of 105 particles were analyzed under these conditions. 50 (48%) were completely condensed clusters, 22 (21%) were partially condensed, and 33 (31%) were naked DNA. (D) Electron micrograph showing sample containing 300 nM Mlh1-Mlh3 + 3.6 nM 2.7 kb circular DNA. Higher concentration of protein induces formation of more condensed protein–DNA clusters (black arrows). Mlh1-Mlh3 protein complexes are also seen in the background of the micrograph. 53 total particles were assessed. Of these, 50 (94%) were completely condensed clusters, 1 (2%) was a partially condensed, and 2 (4%) were naked DNA.