Streptavidin-bound oligonucleotides can be used to determine the directionality of various helicases. Helicase directionality assays were performed as described in "Methods" using the substrates shown at the top (I-IV). In each substrate the longer oligonucleotide is 32P-labeled and streptavidin is marked by a closed circle. Panels A and E, Tag; panels B and F, mtMCM; panels C and G, ecUvrD; panels D and H, ecRecQ. Representative results are shown (A-D) together with a summary with standard deviation of three independent experiments (E-H). The amount of protein (as monomer) used and whether ATP was present or not is indicated in the top of each panel.