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:Because there was no rat ATP5G3 cDNA sequence available in GenBank databases, for ATP5G3 coding sequence information, the rat pancreatic cDNA library was screened via PCR with ATP5G3 gene-specific primers (Table 1) that were designed based on the human ATP5G3 cDNA sequence (U09813) (50).
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