PLANT PHYSIOLOGY , Vol 108, Issue 2 805-812, Copyright © 1995 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Structural Analysis, Plastid Localization, and Expression of the Biotin Carboxylase Subunit of Acetyl-Coenzyme A Carboxylase from Tobacco
B. S. Shorrosh, K. R. Roesler, D. Shintani, F. J. van de Loo and J. B. Ohlrogge
Department of Botany and Plant Pathology, Plant Biology Building, Michigan State University, East Lansing, Michigan 48824-1321
Acetyl-coenzyme A carboxylase (ACCase, EC 6.4.1.2) catalyzes the synthesis
of malonyl-coenzyme A, which is utilized in the plastid for de novo fatty
acid synthesis and outside the plastid for a variety of reactions,
including the synthesis of very long chain fatty acids and flavonoids.
Recent evidence for both multifunctional and multisubunit ACCase isozymes
in dicot plants has been obtained. We describe here the isolation of a
tobacco (Nicotiana tabacum L. cv bright yellow 2 [NT1]) cDNA clone (E3)
that encodes a 58.4-kD protein that shares 80% sequence similarity and 65%
identity with the Anabaena biotin carboxylase subunit of ACCase. Similar to
other biotin carboxylase subunits of acetyl-CoA carboxylase, the E3-encoded
protein contains a putative ATP-binding motif but lacks a biotin-binding
site (methionine-lysine-methionine or methionine-lysine-leucine). The
deduced protein sequence contains a putative transit peptide whose function
was confirmed by its ability to direct in vitro chloroplast uptake. The
subcellular localization of this biotin carboxylase has also been confirmed
to be plastidial by western blot analysis of pea (Pisum sativum), alfalfa
(Medicago sativa L.), and castor (Ricinus communis L.) plastid
preparations. Northern blot analysis indicates that the plastid biotin
carboxylase transcripts are expressed at severalfold higher levels in
castor seeds than in leaves.
