Abstract
Preselection digests are a common strategy to reduce the background in the ligation step of molecular cloning. However, choosing fitting restriction enzymes by hand is not trivial and may lead to errors, potentially costing a lot of time and work. We therefore created preselector.uni-jena.de (https://preselector.uni-jena.de/), a free online tool to find such restriction enzymes. The tool uses regular expressions to find recognition sites of restriction enzymes in the DNA sequences provided by the user. This new tool compares the sets of restriction sites and reports the enzymes that cut one sequence but not the other sequences to the user. These enzymes are then the ones suitable for a preselection digest. Thus, preselector.uni-jena.de is a fast, reliable, and free-to-use tool to help researchers designing preselection digestion strategies for their cloning.