A Rapeseed Cold-Inducible Transcript Encodes a Phosphoenolpyruvate Carboxykinase

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Abstract
We have isolated a clone corresponding to a new cold-regulated gene from a cDNA library made from rapeseed (Brassica napus cv Samourai) cold-acclimated etiolated seedlings. Sequence analysis and homology searches showed that this clone encodes a protein highly homologous to the ATP-dependent phosphoenolpyruvate carboxykinase (PEPCK; EC 4.1.1.49) from Saccharomyces cerevisiae, Trypanosoma, Rhizobium sp., and Escherichia coli; we refer to the B. napus clone as BnPEPCK. A potential ATP-binding site existing in all PEPCK proteins was also found in BnPEPCK. Although there was a basal expression of BnPEPCK in seedlings grown at control, room temperature, the steady-state level of the transcripts increased at 4[deg]C and decreased to normal levels when the seedlings were returned to control temperature (22[deg]C). Using antibodies made against a recombinant histidine-BnPEPCK fusion protein, we demonstrated that BnPEPCK protein level is correlated with the accumulation of the BnPEPCK transcript.