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:Most animal and plant D-type cyclins have the amino acid motif LxCxE near their amino terminus which is required for binding to the RBR protein (Ewen et al. 1993; Soni et al. 1995; Menges et al. 2007).
Category: