Document Detail

The testis-specific high-mobility-group protein, a phosphorylation-dependent DNA-packaging factor of elongating and condensing spermatids.
MedLine Citation:
PMID:  8668189     Owner:  NLM     Status:  MEDLINE    
Mammalian spermiogenesis is characterized by a striking restructuring of the spermatid chromatin caused by the replacement of nucleohistones with transition proteins and their subsequent replacement with nucleoprotamines. The onset of nuclear elongation and chromatin condensation in spermatids is accompanied by a general decrease in the transcriptional activity of the DNA. A recently identified testis-specific high-mobility-group (tsHMG) protein, similar to the human mitochondrial transcription factor I and to the linker-associated protein delta of Tetrahymena thermophila micronuclei, is thought to play a structural role in this process. We confirm by immunoblot analysis of fractionated germ cells that the presence of tsHMG is restricted to transcriptionally quiescent elongating and condensing spermatids. Purified recombinant tsHMG protein displays preferential binding to supercoiled plasmid DNA, which reversibly protects the DNA against the DNA-relaxing activity of eukaryotic topoisomerase I and also impairs the transcriptional activity of this template when assayed in vitro. The tsHMG protein can also introduce negative supercoils into a relaxed plasmid substrate in a topoisomerase I-dependent manner. We also show that the tsHMG protein is the substrate of a Ca2+-phospholipid-dependent protein kinase (protein kinase C) present in testis extracts of adult mice and demonstrate that phosphorylation by protein kinase C is required for both the DNA-binding and the topoisomerase I-dependent supercoiling activities of tsHMG. Our results support the hypothesis that the spermatid tsHMG protein is a topological factor (transition protein) that can modulate the activity of topoisomerase I. This activity could contribute to the important transition in chromatin structure which leads to the decrease in DNA metabolism observed at the early stages of spermatid elongation.
N Alami-Ouahabi; S Veilleux; M L Meistrich; G Boissonneault
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Molecular and cellular biology     Volume:  16     ISSN:  0270-7306     ISO Abbreviation:  Mol. Cell. Biol.     Publication Date:  1996 Jul 
Date Detail:
Created Date:  1996-08-08     Completed Date:  1996-08-08     Revised Date:  2009-11-18    
Medline Journal Info:
Nlm Unique ID:  8109087     Medline TA:  Mol Cell Biol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  3720-9     Citation Subset:  IM    
Department of Biochemistry, Faculty of Medicine, University of Sherbrooke, Quebec, Canada.
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MeSH Terms
DNA, Superhelical / metabolism
DNA-Binding Proteins / metabolism
Gene Expression Regulation
High Mobility Group Proteins / biosynthesis,  isolation & purification,  metabolism*
Mitochondrial Proteins*
Nuclear Proteins*
Plasmids / metabolism
Protozoan Proteins / metabolism
Recombinant Proteins / isolation & purification,  metabolism
Spermatids / physiology*
Spermatocytes / metabolism
Spermatogonia / metabolism
Tetrahymena thermophila / metabolism
Transcription Factors / metabolism
Transcription, Genetic
Grant Support
Reg. No./Substance:
0/DNA, Superhelical; 0/DNA-Binding Proteins; 0/High Mobility Group Proteins; 0/Mitochondrial Proteins; 0/Nuclear Proteins; 0/Protozoan Proteins; 0/Recombinant Proteins; 0/TFAM protein, human; 0/Tfam protein, mouse; 0/Transcription Factors; 0/mitochondrial transcription factor A

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