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Molecular and Cellular Biology, July 2008, p. 4434-4444, Vol. 28, No. 13
0270-7306/08/$08.00+0     doi:10.1128/MCB.00543-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Ydj1 Protects Nascent Protein Kinases from Degradation and Controls the Rate of Their Maturation{triangledown}

Atin K. Mandal,1,2 Nadinath B. Nillegoda,1 Jennifer A. Chen,1 and Avrom J. Caplan1,2*

Department of Pharmacology and Systems Therapeutics, Mount Sinai School of Medicine, New York, New York 10029,1 Department of Biology, City College New York, New York 100312

Received 3 April 2007/ Accepted 15 April 2008

Ydj1 is a Saccharomyces cerevisiae Hsp40 molecular chaperone that functions with Hsp70 to promote polypeptide folding. We identified Ydj1 as being important for maintaining steady-state levels of protein kinases after screening several chaperones and cochaperones in gene deletion mutant strains. Pulse-chase analyses revealed that a portion of Tpk2 kinase was degraded shortly after synthesis in a ydj1{Delta} mutant, while the remainder was capable of maturing but with reduced kinetics compared to the wild type. Cdc28 maturation was also delayed in the ydj1{Delta} mutant strain. Ydj1 protects nascent kinases in different contexts, such as when Hsp90 is inhibited with geldanamycin or when CDC37 is mutated. The protective function of Ydj1 is due partly to its intrinsic chaperone function, but this is minor compared to the protective effect resulting from its interaction with Hsp70. SIS1, a type II Hsp40, was unable to suppress defects in kinase accumulation in the ydj1{Delta} mutant, suggesting some specificity in Ydj1 chaperone action. However, analysis of chimeric proteins that contained the chaperone modules of Ydj1 or Sis1 indicated that Ydj1 promotes kinase accumulation independently of its client-binding specificity. Our results suggest that Ydj1 can both protect nascent chains against degradation and control the rate of kinase maturation.

* Corresponding author. Mailing address: Department of Biology, City College New York, Convent Avenue at 138th Street, New York, NY 10031. Phone: (212) 650-8614. Fax: (212) 650-8585. E-mail: acaplan{at}sci.ccny.cuny.edu

{triangledown} Published ahead of print on 28 April 2008.

Molecular and Cellular Biology, July 2008, p. 4434-4444, Vol. 28, No. 13
0270-7306/08/$08.00+0     doi:10.1128/MCB.00543-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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