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:NSP1 also binds specifically to all rotavirus mRNAs [4, 15], and while the sequence necessary for NSP1 binding has not been precisely identified, it is known to be located near the 5′-end, since gene 5 mRNA probes containing the first 278 nucleotides are sufficient for NSP1 binding [15].
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