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:Plasmids encoding for hemagglutinin-tagged JNK1 (HA-JNK1) and c-Jun (amino acids 5–89) fused to glutathione S-transferase (GST-c-Jun) were described previously (15).
Category: