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:RO91 contains a translational fusion that harbors the turnover element susceptible to proteolysis [genotype, MC4100 (ŒªRZ5:rpoS742::lacZ)hybr] (MUFFLER et al. 1996).
Category: