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:Previous work from our laboratory and others has shown that Ebp2, Brx1, Nop12, and r-protein L8 associate with preribosomes during early steps of 60S subunit assembly and coimmunoprecipitate (co-IP) early 66S pre-rRNA intermediates (25, 26, 28).
Category: