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:Following digestion, the cDNA was then cloned into an enhanced green fluorescent protein (eGFP; Clontech, Mountain View, CA) vector creating a plasmid where eGFP was linked to TDAG51 protein (termed eGFP-TDAG51), as previously described (31).
Category: