STRUCTURE OF A GENE ENCODING A CYTOSOLIC ACETYL-COA CARBOXYLASE OF HEXAPLOID WHEAT

An entire gene encoding wheat (var. Hard Red Winter Tam 107) acetyl-Co A carboxylase [ACCase; acetyl-CoA:carbon-dioxide ligase (ADP-forming), EC 6.4.1.2] has been cloned and sequenced. Comparison of the 12-kb ge nomic sequence with the 7.4-kb cDNA sequence reported previously revea led 29 introns. Within the coding region, the exon sequence is 98% ide ntical to the known wheat cDNA sequence, A second ACCase gene was iden tified by sequencing fragments of genomic clones that include the firs t two exons and the first intron. Additional transcripts were detected by 5' and 3' RACE analysis (rapid amplification of cDNA ends). One se t of transcripts had a 5' end sequence identical to the cDNA found pre viously and another set was identical to the gene reported here. The 3 ' RACE clones fall into four distinguishable sequence sets, bringing t he number of ACCase sequences to six. None of these cDNA or genomic cl ones encodes a chloroplast targeting signal. Identification of six dif ferent sequences suggests that either the cytosolic ACCase genes are d uplicated in the three chromosome sets in hexaploid wheat or that each of the six alleles of the cytosolic ACCase gene has a readily disting uishable DNA sequence.