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:The PlyG binding domain (PlyG) was amplified by PCR from a Wb phage template with indicated primers and cloned in-frame with the 39 end of gfpmut2 in plasmid pBAD24 as described previously [46].
Category: