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 observations that P30 (33, 53) and vRNA (48) colocalize with the microtubule cytoskeleton and that the abilities of several P30 mutants to associate with the microtubule cytoskeleton and to support cell-to-cell movement showed a strict correlation (7, 8), indeed suggest a role for the microtubule cytoskeleton in TMV cell-to-cell transport.
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