A RAPESEED COLD-INDUCIBLE TRANSCRIPT ENCODES A PHOSPHOENOLPYRUVATE CARBOXYKINASE

We have isolated a clone corresponding to a new cold-regulated gene fr om a cDNA library made from rapeseed (Brassica napus cv Samourai) cold -acclimated etiolated seedlings. Sequence analysis and homology search es showed that this clone encodes a protein highly homologous to the A TP-dependent phosphoenolpyruvate carboxykinase (PEPCK; EC 4.1.1.49) fr om Saccharomyces cerevisiae, Trypanosoma, Rhizobium sp., and Escherich ia coli; we refer to the B. napus clone as BnPEPCK. A potential ATP-bi nding site existing in all PEPCK proteins was also found in BnPEPCK. A lthough there was a basal expression of BnPEPCK in seedlings grown at control, room temperature, the steady-state level of the transcripts i ncreased at 4 degrees C and decreased to normal levels when the seedli ngs were returned to control temperature (22 degrees C). Using antibod ies made against a recombinant histidine-BnPEPCK fusion protein, we de monstrated that BnPEPCK protein level is correlated with the accumulat ion of the BnPEPCK transcript.