ISSN:
0730-2312
Keywords:
C. elegans
;
E. coli
;
immunoreactive degradation intermediates
;
affinity-purified protein
;
ubiquitin
;
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
Notes:
The product of an integrated transgene provides a convenient and cell-specific reporter of intracellular protein catabolism in 103 muscle cells of the nematode Caenorhabditis elegans. The transgene is an in-frame fusion of a 5′-region of the C. elegans unc-54 (muscle myosin heavy-chain) gene to the lacZ gene of Escherichia coli [Fire and Waterston (1989): EMBO J 8:3419-3428], encoding a 146-kDa fusion polypeptide that forms active β-galactosidase tetramers. The protein is stable in vivo in well-fed animals, but upon removal of the food source it is inactivated exponentially (t1/2 = 17 h) following an initial lag of 8 h. The same rate constant (but no lag) is observed in animals starved in the presence of cycloheximide, implying that inactivation is catalyzed by pre-existing proteases. Both the 146-kDa fusion polypeptide (t1/2 = 13 h) and a major 116-kDa intermediate (t1/2 = 7 h) undergo exponential physical degradation after a lag of 8 h. Degradation is thus paradoxically faster than inactivation, and a number of characteristic immunoreactive degradation intermediates, some less than one-third the size of the parent polypeptide, are found in affinity-purified (active) protein. Some of these intermediates are conjugated to ubiquitin. We infer that the initial proteolytic cleavages occur in the cytosol, possibly by a ubiquitin-mediated proteolytic pathway and do not necessarily inactivate the fusion protein tetramer. J. Cell. Biochem. 67:143-153, 1997. © 1997 Wiley-Liss, Inc.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
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