Document Detail

Cloning and functional expression of the small subunit of acetolactate synthase from Nicotiana plumbaginifolia.
MedLine Citation:
PMID:  10487214     Owner:  NLM     Status:  MEDLINE    
Acetolactate synthase (ALS) is the first committed step of branched-chain amino acid biosynthesis in plants and bacteria. The bacterial holoenzyme has been well characterized and is a tetramer of two identical large subunits (LSUs) of 60 kDa and two identical small subunits (SSUs) ranging in molecular mass from 9 to 17 kDa depending on the isozyme. The enzyme from plants is much less well characterized. Attempts to purify the protein have yielded an enzyme which appears to be an oligomer of LSUs, with the potential existence of a SSU for the plant enzyme remaining a matter of considerable speculation. We report here the discovery of a cDNA clone that encodes a SSU of plant ALS based upon the homology of the encoded peptide with various bacterial ALS SSUs. The plant ALS SSU is more than twice as large as any of its prokaryotic homologues and contains two domains that each encode a full-length copy of the prokaryotic SSU polypeptide. The cDNA clone was used to express Nicotiana plumbaginifolia SSU in Escherichia coli. Mixing a partially purified preparation of this SSU with the LSU of ALS from either N. plumbaginifolia or Arabidopsis thaliana results in both increased specific activity and increased stability of the enzymic activity. These results are consistent with those observed for the bacterial enzyme in similar experiments and represent the first functional demonstration of the existence of a SSU for plant ALS.
H P Hershey; L J Schwartz; J P Gale; L M Abell
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Publication Detail:
Type:  Comparative Study; Journal Article    
Journal Detail:
Title:  Plant molecular biology     Volume:  40     ISSN:  0167-4412     ISO Abbreviation:  Plant Mol. Biol.     Publication Date:  1999 Jul 
Date Detail:
Created Date:  1999-10-04     Completed Date:  1999-10-04     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  9106343     Medline TA:  Plant Mol Biol     Country:  NETHERLANDS    
Other Details:
Languages:  eng     Pagination:  795-806     Citation Subset:  IM    
Agricultural Products Department, E.I. du Pont de Nemours, Inc., Stine-Haskell Research Laboratory, Newark, DE 19714, USA.
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MeSH Terms
Acetolactate Synthase / chemistry,  genetics*,  metabolism
Amino Acid Sequence
Base Sequence
Cloning, Molecular
Escherichia coli / enzymology
Genetic Vectors
Isoenzymes / chemistry,  genetics,  metabolism
Macromolecular Substances
Molecular Sequence Data
Molecular Weight
Plants, Toxic*
Recombinant Fusion Proteins / biosynthesis,  chemistry,  metabolism
Seeds / enzymology
Sequence Alignment
Sequence Homology, Amino Acid
Tobacco / enzymology*,  genetics*
Reg. No./Substance:
0/Isoenzymes; 0/Macromolecular Substances; 0/Recombinant Fusion Proteins; EC Synthase

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