Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:A number of studies, using closed DNA minicircles or plasmids that lack free ends, have shown that Ku also exhibits sequence-specific DNA binding to regulatory DNA elements effecting gene transcription and DNA replication [13, 54].
Category: