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:Activated PERK blocks protein synthesis by phosphorylating eIF2α [13], and the phosphorylation makes ATF4, a transcription factor, to translocate into the nucleus, and induce the transcription of genes needed to restore ER homeostasis (i.
Category: