CHARACTERIZATION OF A CDNA-ENCODING ARABIDOPSIS-THALIANA INOSITOL 1,3,4-TRISPHOSPHATE 5 6-KINASE/

We have sequenced and recombinantly expressed as a fusion protein an e xpressed sequence tag clone (GB Z25963) from Arabidopsis thaliana that represents the plant homologue of human inositol 1,3,4 trisphosphate 5/6-kinase. The 1365 base pair clone has an open reading frame of 960 base pairs that predicts a protein product of 36.2 kDa, with a pi of 6 .1. There is no polyadenylation signal or poly (A) tail, suggesting th at additional 3' sequence remains to be identified. The amino acid seq uence is 30% identical to the human protein, There are several short r egions with particularly high degrees of identity between the human an d Arabidopsis protein sequences, and these may be useful in identifyin g the active site of the enzyme, The expressed sequence tag was expres sed as a fusion protein in Escherichia coli, with a carboxyl terminal deletion removing one region of high identity between the two proteins , The protein product of this construct was found to have inositol 1,3 ,4-trisphosphate 5/6-kinase activity, The Arabidopsis enzyme produced both inositol 1,3,4,6-tetrakisphosphate and inositol 1,3,4,5-tetrakisp hosphate as products in a ratio of 1:3, in contrast with the human enz yme which gives a product ratio of 3:1, (C) 1997 Academic Press.