Universal substrate to determine helicase directionality using streptavidin-bound oligonucleotides. Helicase directionality assays were performed as described in "Methods" using the substrates shown at the top. The 32P-labeled oligonucleotides are marked with asterisks and streptavidin is marked with large closed circles. Representative results are shown together with a summary and standard deviation of three independent experiments. The amount of protein (as hexamer) used and whether ATP was present or not is indicated at the top of each panel.