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:…Smt3 and Ubc9 1379
© 2004 Blackwell Publishing Ltd, Molecular Microbiology, 51, 1375–1387
Proteolysis of cyclin and non-cyclin APC/C substrates is impaired in ubc9-2 and smt3-331 mutants
Previous results described a role for Ubc9 in the degradation of cyclins Clb2 and Clb5 (Seufert et al., 1995).
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