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B Burr

Publications and source records attributed to B Burr.

32 records · Page 2Linked to original sources
PubMed1982

Ds controlling elements of maize at the shrunken locus are large and dissimilar insertions.

A recombinant clone for the wild-type gene of sucrose synthetase has been selected. Subclones of the genomic clone were made and used as probes to construct a restriction map of the wild-type locus. The transcribed region and the direction of transcription in the map were also determined. Four Ds-induced mutations of the locus that were isolated by B. McClintock were analyzed and partially mapped. Two mutations contain insertions of approximately 20 kb of foreign DNA into the transcribed region; two others are at the 5' end of the gene. There are profound differences in the restriction maps of the Ds elements in the mutants analyzed, even though these elements have a common genetic origin and are separated by only a few generations. Comparison of one pair of closely related Ds elements indicates that these differences may be the result of extensive internal rearrangements. Exchange with other elements in the genome remains an alternative possibility. A revertant of one of the Ds-induced mutations has maintained a 21-22 kb insert at the same location in the transcribed region. This insert differs from its predecessor by extensive rearrangement in two thirds of its length. Part, or all, of this rearrangement presumably permits functional expression of the gene.

Chromosome Mapping↗
PubMed1982

Three mutations in Zea mays affecting zein accumulation: a comparison of zein polypeptides, in vitro synthesis and processing, mRNA levels, and genomic organization.

We studied three mutations, opaque-2 (o2), opaque-7 (o7), and floury-2(fI2), each of which causes a depression in zein synthesis. We examined the processing efficiencies of the rough endoplasmic reticulum membranes in vitro, the levels of RNA transcription using cloned zein probes, and the genomic organization of the zein sequences as possible sites for the genetic defects. The results obtained indicate that the steps in prezein translation and processing occurring on the protein body membranes are not accountable for the lowered zein content in any of the mutations. The o2 mutation that typically shows a paucity of 22.5-kdalton zein polypeptides was found to have a concomitant reduction in a particular subgroup of mRNAs coding for this size class. Southern analyses suggest that the o2 mutation is not the result of a large deletion of tandem-linked zein genes.

Endoplasmic Reticulum↗
PubMed1981

In vitro uptake and processing of prezein and other maize preproteins by maize membranes.

A cell-free, mRNA-dependent system has been developed for the translation and processing of zein preproteins. A rough endoplasmic reticulum (RER)-enriched fraction, isolated by sucrose density gradients, can be treated with micrococcal nuclease to destroy endogenous messages. When these membranes are added to a wheat germ protein-synthesizing system together with zein mRNA, synthesis and processing of the polypeptides to the mature products takes place. The RER fraction from the endosperm has a different protein composition than that prepared from either the shoot or nucellar tissue and processes prezein more efficiently. The cleavage of the preproteins appears to be a cotranslational step as the completed preprotein chains cannot be processed, although they can be taken up to a limited extent. This small uptake, or absorption, or unprocessed zein seems to be an artifact and may be related to the unusual solubility properties of zein. Finally a sodium dodecyl sulfate (SDS)-urea polyacrylamide gel system has been developed which is particularly suited for the separation of low molecular weight proteins (less than 10,000 daltons). Using this method, we examined the products of in vitro zein processing and detected no presequence polypeptides. This suggests that the zein cleavage proteinase is probably an exopeptidase.

Cell-Free System↗
PubMed1978

Purification and translation of zein messenger RNA from maize endosperm protein bodies.

The messenger RNAs coding for the zein storage protein have been purified from other contaminating RNAs. The average molecular lengths are 1.1-1.2 kilobases, as determined by polyacrylamide gel electrophoresis and by electron microscopy. Products of messenger-dependent protein synthesis in vitro appear to be 1100 and 2000 daltons heavier than the native polypeptides. Zein is like secretory proteins in having a precursor with an additional amino-terminal sequence. Although only one mRNA is seen in polyacrylamide gel electrophoresis, the combined size of the polypeptide products formed exceeds the coding capacity for one message of the size determined in this study. This suggests that there are at least two mRNAs of similar sizes for the zein polypeptides rather than one dicistronic message.

Journal Article↗
PubMed1976

Homoserine kinase from Escherichia coli K12.

Homoserine kinase was purified to apparent homogeneity from a derepressed strain of Escherichia coli K12, using standard fractionation techniques. It is a dimer (Mr = 60000) composed of apparently identical polypeptide chains (Mr = 29000). Its amino acid composition and N-terminal sequence have been determined. L-Threonine is a competitive inhibitor of the substrate L-homoserine; this inhibition is straighforward and shows no sign of co-operativity. Evidence is presented that homoserine and threonine bind to the same site of this non-allosteric enzyme. The binding of homoserine and threonine can also be studied by difference spectroscopy; the latter studies reveal an unexpected effect of magnesium ions, which might be the basis for the unusual high Mg2+ requirement for optimal enzyme reaction.

Amino Acid Sequence↗
PubMed1976

Zein synthesis in maize endosperm by polyribosomes attached to protein bodies.

The protein bodies in maize endosperm are the sites of zein deposition. They are single membrane-bound vesicles with polysomes associated with the exterior surface of the membrane. These protein bodies were isolated by sucrose density gradients and characterized by electron microscopy and polyacrylamide gel electrophoresis. Polyribosomes dissociated from the surface of the membrane by detergent treatment were placed into an amino-acid incorporating system. Based on alcohol solubility, amino-acid composition, and molecular weight distribution, the product synthesized appeared to be largely, or entirely, zein. This suggests the existence of components which are specific for the synthesis of zein at the protein body membrane surface.

Cell-Free System↗
PubMed1975

Maize alpha-glucan phosphorylase.

The major isozyme of alpha-glucan phosphorylase from developing maize seeds has been purified to homogeneity as verified by gel electrophoresis, ultracentrifugation and immunoprecipitation. The enzyme appears to be dimeric and has an estimated molecular weight of 223000 +/- 10000 based on ultracentrifugation, dodecylsulfate gel electrophoresis, and pyridoxal phosphate content. Adenosine diphosphoglucose appears to be a physiologically important inhibitor and interacts with the enzyme to give sigmoid kinetics when glucose 1-phosphate is the variable substrate. There are no properties of the enzyme which distinguish it from other phosphorylases as having a primarily synthetic role.

Adenosine Diphosphate Glucose↗
PubMed1975

Evolution of biosynthetic pathways: immunological approach.

Through the use of specific immunoadsorbent columns, it is shown that Escherichia coli aspartokinase I-homoserine dehydrogenase I, aspartokinase II-homoserine dehydrogenase II, aspartokinase III, and homoserine kinase, enzymes involved in the same complex biosynthetic pathway, share antigenic determinants. This raises the question of a common origin for the four cibtenoirart kinases. (Aspartate kinase or ATP:L aspartate 4-phosphotransferase, EC 2.7.2.4; homoserine dehydrogenase or Lhomoserine:NADP oxidoreductase, EC 1.1.1.3; homoserine kinase or ATP:L-homoserine O-phosphotransferase, EC 2.7.1.39.)

Alcohol Oxidoreductases↗
PubMedDate not supplied

Chromosomal assignment of microsatellite loci in cotton.

Microsatellite markers or simple sequence repeats (SSRs) represent a new class of genetic markers for cotton (Gossypium sp.). Sixty-five SSR primer pairs were used to amplify 71 marker loci and genotype 13 monosomic and 27 monotelodisomic cotton cytogenetic stocks. Forty-two SSR loci were assigned to cotton chromosomes or chromosome arms. Thirty SSRs were not located to specific chromosomes in this study. Nineteen marker loci were shown to occur on the A subgenome and 11 on the D subgenome by screening accessions of G. herbaceum (2n = 2x = 26 = 2A1) and G. raimondii (2n = 2x = 26 = 2D5). The aneuploid stocks proved to be very powerful tools for localizing SSR markers to individual cotton chromosomes. Multiplex PCR bins of the SSR primers and semiautomated detection of the amplified products were optimized in this experiment. Thirteen multiplex PCR bins were optimized to contain an average of 4 SSR primer pairs per bin. This provides a protocol for high-throughput genotyping of cotton SSRs that improves the efficiency of genetic mapping and marker-assisted programs utilizing SSR markers.

Alleles↗