Plant chromosomal high mobility group (HMG) proteins.
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Amino Acid Sequence↗
Biomedical subjects
K D Grasser
Publications and source records attributed to K D Grasser.
Stability of the maize chromosomal high-mobility-group proteins, HMGa and HMGb, in vivo.
Chromosomal non-histone high-mobility-group (HMG) proteins represent essential components of eukaryotic chromatin and have also been isolated from a variety of plants. In maize, studies on structure and function of the two larger of the four major HMG proteins have recently been performed and are now extended by analysis of their in vivo stability using pulse-chase experiments in a cell suspension culture. The half-life of the analyzed HMGa and HMGb proteins was found to be 65 h or more than 78 h, respectively.
Cells, Cultured↗
The maize chromosomal HMGa protein recognizes structural features of DNA and increases DNA flexibility.
The abundant maize high-mobility group protein HMGa belongs to the chromosomal, non-histone proteins and consists of a basic region containing the HMG-box DNA-binding domain and a highly acidic carboxy-terminal tail. The full-length HMGa protein and a truncated version lacking the acidic tail were synthesized in Escherichia coli and tested for their ability to induce DNA-bending in a ligase mediated circularization assay with short DNA fragments. It is shown that the recombinant HMGa protein as well as its truncated form efficiently cause circularization of the tested DNA fragments without an obvious requirement for stable DNA-binding. They bind furthermore preferentially to A/T-rich linear DNA or bent DNA structures such as four-way junctions and DNA minicircles. The DNA-binding properties and the ability to increase DNA flexibility suggest a general role of the HMGa protein in assisting the formation of nucleoprotein complexes, possibly by facilitating interactions of proteins bound to adjacent DNA sites.
Base Sequence↗
Stimulatory effect of the maize HMGa protein on reporter gene expression in maize protoplasts.
The high mobility group (HMG) proteins represent a class of chromosomal non-histone proteins with an assumed influence on transcription. In this context, the effect of the maize HMGa protein on reporter gene expression was examined. Transient co-transformation experiments in maize protoplasts with plasmid constructs directing the synthesis of the maize HMGa protein and with a luciferase reporter plasmid demonstrated a stimulatory effect of the HMGa protein on the reporter gene expression. Additional experiments with HMGa deletion constructs indicated that the HMG-Box DNA-binding motif is important for the observed effect, while the acidic carboxy-terminal domain of the HMGa protein appears to be dispensable.
Gene Expression Regulation, Enzymologic↗
Comparative analysis of chromosomal HMG proteins from monocotyledons and dicotyledons.
Chromosomal high-mobility-group (HMG) proteins occur ubiquitously in eukaryotes and their common structural and biochemical features indicate a critical role. In this context, we compared structural and functional aspects of HMG proteins from the monocotyledonous plant maize and the dicotyledonous plant Vicia faba. Besides biochemical similarities and immunological differences found between these proteins, the isolation and characterization of a cDNA encoding the V. faba homologue of the maize HMGa protein revealed great similarities between these two proteins, including the HMG-box DNA-binding motif and an acidic domain. Therefore, like the maize HMGa protein, the V. faba HMG protein belongs to the vertebrate HMG1 family, which consists of HMG proteins and transcription factors of various eukaryotes.
Amino Acid Sequence↗
Repeat units from a maize rDNA external spacer region exhibit DNA curvature and interact with high-mobility-group proteins.
The 3-kb external spacer from a maize (Zea mays L. cv. A619) nuclear rRNA gene unit which contains nine highly homologous 200-bp repeat elements was found to include a region with DNA-curvature properties. The centre of curvature was localized within repeats 5 and 6 using a circular permutation assay. A 60-bp-long subfragment of this region was found to interact with nuclear proteins, including high-mobility-group (HMG) proteins, and with the maize HMGa protein synthesized in Escherichia coli from a recombinant plasmid. The potential influence of the binding of the HMG proteins on the conformation of this subfragment was studied with a permutation assay based on a bending vector.
Base Sequence↗
Phylogenetic relationships of HMG box DNA-binding domains.
HMG boxes were initially identified as DNA-binding domains of the human RNA polymerase I (pol I) transcription factor hUBF and the animal high-mobility-group (HMG) protein family HMG1. Since then, numerous sequences of HMG-box-containing HMG proteins and other DNA-binding proteins from several species have become available. By sequence comparisons of a selected range of HMG boxes from these proteins and the construction of phylogenetic trees we show that the HMG box is highly conserved between DNA-binding proteins of organisms from all three eukaryotic kingdoms and that HMG boxes are linked by distinct evolutionary relationships. In addition, most HMG boxes display comparable hydropathy profiles and amino acid arrangements, which could serve as nuclear targeting sequences.
Amino Acid Sequence↗
Isolation and characterization of maize cDNAs encoding a high mobility group protein displaying a HMG-box.
cDNAs encoding a nonhistone chromosomal high mobility group (HMG) protein corresponding to the animal HMG1 family were isolated from a maize cDNA library using an immunoscreening approach. The cDNAs revealed an open reading frame of 471 base pairs together with 413 base pairs of flanking region, in agreement with the size of mRNA detected by Northern analysis of maize endosperm RNA. Like its animal counterparts the 17146 Da maize HMG protein contains a basic aminoterminus and an acidic carboxyterminus. The HMG-box region of this plant HMG protein shows striking sequence similarity to members of the vertebrate HMG1 family. Based on Southern blot hybridization analysis of genomic DNA, the isolated cDNA appears to be derived from a single or low copy gene.
Amino Acid Sequence↗
Maize high mobility group proteins bind to CCAAT and TATA boxes of a zein gene promoter.
A 216-base pair promoter fragment of the 19-kDa zein storage protein gene pMS1, containing the CCAAT and TATA boxes, was analyzed for its in vitro interactions with purified high mobility group (HMG) proteins from maize endosperm tissue. It was found that the HMG proteins display a preferential binding of A/T-rich DNA regions like their animal counterparts, although the A/T content seems not to be the only determinant for binding specificity. Surprisingly, a specific binding of the HMG proteins occurs at the CCAAT and the TATA boxes as indicated by footprinting experiments.
Base Sequence↗
Multiple proteins bind to the P2 promoter region of the zein gene pMS1 of maize.
A 216 bp promoter fragment of the 19 kDa protein zein gene pMS1, containing the CCAAT and TATA boxes, was analysed by a variety of techniques for in vitro interactions with nuclear proteins from endosperm tissue. HMG proteins were found to form stable complexes with these A/T-rich promoter sequences and several specific DNA-binding proteins appear to be involved in the formation of DNA-protein complexes with this fragment. A 29 bp region spanning the two CCAAT boxes was protected from DNase I digestion in footprinting experiments.
Base Sequence↗
A nuclear casein type II kinase from maize endosperm phosphorylating HMG proteins.
A casein kinase of the type II was isolated and enriched from nuclear lysates of maize endosperm tissue. The kinase activity requires 10 mM Mg2+ for maximal activity, can utilize either ATP or GTP as phosphate donors and is inhibited by polyamines, heparin and monovalent cations. A substrate specificity of the kinase activity towards specific nuclear proteins is indicated by its phosphorylation of high mobility group (HMG) proteins isolated from endosperm and its lack of accepting histones as protein substrates.
Animals↗