Mapping and expression of a bifunctional thymidylate synthase, dihydrofolate reductase gene from maize.
A bifunctional gene (ZmDHFR-TS) encoding dihydrofolate reductase (DHFR) and thymidylate synthase (TS) was cloned from a Zea mays cDNA library. Both of these enzymes are involved in nucleotide biosynthesis, specifically in the formation of thymidine monophosphate (TMP). Comparison of the deduced amino acid sequence with DHFR-TS sequences from three other plant sources revealed over 75% similarity and motifs typical of DHFR-TS proteins. Two copies of the gene were mapped to chromosomes 2 and 4. This represents the first DHFR-TS gene cloned from a monocotyledonous plant. Expression of ZmDHFR-TS was examined in developing kernels and various tissues of maize by RNA gel blot hybridization analysis in order to determine the relationship between expression of this gene and DNA synthesis. RNA transcripts for ZmDHFR-TS accumulated to high levels in developing maize kernels when endosperm cells were undergoing endoreduplication and cell division. Meristematic maize tissues had high levels of ZmDHFR-TS mRNA, but transcripts were barely detectable in RNA isolated from the root elongation zone and from mature leaf tissues.
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Dept. of Botany, North Carolina State University, Raleigh 27695-7612, USA.
Robertson
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D000595:Amino Acid Sequence; D015152:Blotting, Northern; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D018507:Gene Expression Regulation, Developmental; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000235:genetics*; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D012639:Seeds / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D017422:Sequence Analysis, DNA; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics*; D013940:Thymidylate Synthase / Q000235:genetics*; D014018:Tissue Distribution; D003313:Zea mays / Q000201:enzymology / Q000235:genetics*
D018076:DNA, Complementary; D009097:Multienzyme Complexes; D018749:RNA, Plant; C056930:thymidylate synthase-dihydrofolate reductase; D013762:Tetrahydrofolate Dehydrogenase; D013940:Thymidylate Synthase