Abstract
Aspartate kinase (AK) and homoserine dehydrogenase (HSDH) are enzymes in the aspartate-derived amino acid biosynthetic pathway. Recent biochemical evidence indicates that an AK-HSDH bifunctional enzyme exists in maize (Zea mays L). In this report, we characterize three genes that encode subunits of AK-HSDH. Two cDNAs, pAKHSDH1 and pAKHSDH2, containing the full-coding sequence, and one partial cDNA, pAKHSDH3, encode amino acid sequences similar to the reported monofunctional AK and HSDH enzymes from prokaryotes and yeast (Saccharomyces cerevisiae) and to AK-HSDH bifunctional enzymes of prokaryotes, yeast, carrot (Daucus carota), and Arabidopsis thaliana. Immunological and biochemical analyses verify that the cDNAs encode AK-HSDH and indicate that both the AK and HSDH activities are feedback inhibited by threonine. RNA blots identify a 3.2-kb transcript in all maize tissues examined. pAKHSDH1 and pAKHSDH2 map to chromosomes 4L and 2S, respectively. This study shows that maize contains AK-HSDH bifunctional enzyme(s) encoded by a small gene family of at least three genes. Maize AK-HSDH has conserved sequences found in communication modules of prokaryotic two-component regulatory systems, which has led us to propose that maize AK-HSDH may be involved in a similar regulatory mechanism.
Original language | English (US) |
---|---|
Pages (from-to) | 1303-1312 |
Number of pages | 10 |
Journal | Plant physiology |
Volume | 106 |
Issue number | 4 |
DOIs | |
State | Published - Dec 1994 |