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:GFP-Pex34p, like the peroxisomal matrix protein Pot1p, localized preferentially to a 20,000 × g pellet (20KgP) fraction enriched for mature peroxisomes and some forms of immature peroxisomes (Tam et al., 2003; Vizeacoumar et al., 2003, 2004) (Figure 1B).
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