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:Therefore, we generated a yeast strain in which Scp160p expression is under control of a repressible Tet-off operator, which allows rapid depletion of the protein on addition of doxycyclin (11,25).
Category: