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:However, luciferase gene expression from the IFN-stimulated Mx1 promoter or the SV40 promoter was reduced by PR(1-80)Tx(80-239) but not by Tx(1-80)PR(81-230) (Fig.
Category: