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Fig. 7. Encore is required for proteolysis. (A) Proteasome assays measuring the
hydrolysis of the fluorogenic peptide Suc-LLVYMCA. The 20S-CP proteolysis
activity is not significantly compromised in encore mutant
germarium-enriched extracts at 29°C (yellow) or room temperature (light
blue) compared with wild-type extracts at 29°C (pink). Control assays
contain no substrate peptide (dark blue). (B) Western blot using anti p27
antibodies show that Ubiquitination reactions produce the same
polyubiquitinated p27 forms (arrowheads) in wild-type and encore
mutant extracts. The deubiquitination and degradation reaction is much slower
when encore mutant extract was used as a source of the degradation
machinery. (C) Model of Encore function. Cul1 (pink) is localized to the
fusome (green) in an Encore (blue)-dependent manner (Encore may directly or
indirectly modify Cul1 and thus influence its subcellular localization). Cul1
may serve as an anchor where the SCF E3 complex is assembled and a
phosphorylated substrate (yellow) is recognized and ubiquitinated. The
polyubiquitinated substrate is then recognized by the 19S-recognition
particle. 19S-RP and presumably the 20S-core particle are recruited to the
fusome where the substrate is de-ubiquitinated, unfolded and degraded by the
26S-subunit of the proteasome.
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