Molecular genetics of the maize (Zea mays L.) aspartate kinase-homoserine dehydrogenase gene family.
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.
Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul 55108.
G J
GJ
Muehlbauer
D A
DA
Somers
B F
BF
Matthews
B G
BG
Gengenbach
D000595:Amino Acid Sequence; D000906:Antibodies; D017360:Arabidopsis / Q000235:genetics; D001222:Aspartate Kinase / Q000235:genetics*; D016384:Consensus Sequence; D018744:DNA, Plant / Q000302:isolation & purification / Q000378:metabolism; D018552:Daucus carota / Q000235:genetics; D017343:Genes, Plant; D006715:Homoserine Dehydrogenase / Q000235:genetics*; D008969:Molecular Sequence Data; D005810:Multigene Family; D009842:Oligopeptides / Q000138:chemical synthesis / Q000276:immunology; D010957:Plasmids; D012441:Saccharomyces cerevisiae / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D003313:Zea mays / Q000201:enzymology* / Q000235:genetics*
D000906:Antibodies; D018744:DNA, Plant; D009842:Oligopeptides; D006715:Homoserine Dehydrogenase; D001222:Aspartate Kinase