Precision shock tuning on the national ignition facility

Ignition implosions on the National Ignition Facility [J. D. Lindl et al., Phys. Plasmas 11, 339 (2004)] are underway with the goal of compressing deuterium-tritium fuel to a sufficiently high areal density (ρR) to sustain a self-propagating burn wave required for fusion power gain greater than unity. These implosions are driven with a very carefully tailored sequence of four shock waves that must be timed to very high precision to keep the fuel entropy and adiabat low and ρR high. The first series of precision tuning experiments on the National Ignition Facility, which use optical diagnostics to directly measure the strength and timing of all four shocks inside a hohlraum-driven, cryogenic liquid-deuterium-filled capsule interior have now been performed. The results of these experiments are presented demonstrating a significant decrease in adiabat over previously untuned implosions. The impact of the improved shock timing is confirmed in related deuterium-tritium layered capsule implosions, which show the highest fuel compression (ρR~1.0 g/cm(2)) measured to date, exceeding the previous record [V. Goncharov et al., Phys. Rev. Lett. 104, 165001 (2010)] by more than a factor of 3. The experiments also clearly reveal an issue with the 4th shock velocity, which is observed to be 20% slower than predictions from numerical simulation.

Demonstration of ignition radiation temperatures in indirect-drive inertial confinement fusion hohlraums

We demonstrate the hohlraum radiation temperature and symmetry required for ignition-scale inertial confinement fusion capsule implosions. Cryogenic gas-filled hohlraums with 2.2 mm-diameter capsules are heated with unprecedented laser energies of 1.2 MJ delivered by 192 ultraviolet laser beams on the National Ignition Facility. Laser backscatter measurements show that these hohlraums absorb 87% to 91% of the incident laser power resulting in peak radiation temperatures of T(RAD)=300 eV and a symmetric implosion to a 100 μm diameter hot core.

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.

Induction of pluripotency in human cord blood unrestricted somatic stem cells

OBJECTIVE

Generation of induced pluripotent stem (iPS) cells from human cord blood (CB)-derived unrestricted somatic stem cells and evaluation of their molecular signature and differentiation potential in comparison to human embryonic stem cells.

MATERIALS AND METHODS

Unrestricted somatic stem cells isolated from human CB were reprogrammed to iPS cells using retroviral expression of the transcription factors OCT4, SOX2, KLF4, and C-MYC. The reprogrammed cells were analyzed morphologically, by quantitative reverse transcription polymerase chain reaction, genome-wide microRNA and methylation profiling, and gene expression microarrays, as well as in their pluripotency potential by in vivo teratoma formation in severe combined immunodeficient mice and in vitro differentiation.

RESULTS

CB iPS cells are very similar to human embryonic stem cells morphologically, at their molecular signature, and in their differentiation potential.

CONCLUSIONS

Human CB-derived unrestricted somatic stem cells offer an attractive source of cells for generation of iPS cells. Our findings open novel perspectives to generate human leukocyte antigen-matched pluripotent stem cell banks based on existing CB banks. Besides the obvious relevance of a second-generation CB iPS cell bank for pharmacological and toxicological testing, its application for autologous or allogenic regenerative cell transplantation appears feasible.

Lime pretreatment of switchgrass

Lime (calcium hydroxide) was used as a pretreatment agent to enhance the enzymatic digestibility of switchgrass. After studying many conditions, the recommended pretreatment conditions are: time = 2 h, temperature = 100 degrees C and 120 degrees C, lime loading = 0.1 g Ca(OH)(2)/g dry biomass, water loading = 9 mL/g dry biomass. Studies on the effect of particle size indicate that there was little benefit of grinding below 20 mesh; even coarse particles (4-10 mesh) digested well. Using the recommended pretreatment conditions, the 3-d reducing sugar yield was five times that of untreated switchgrass, the 3-d total sugar (glucose + xylose) yield was seven times, the 3-d glucose yield was five times, and the 3-d xylose yield was 21 times. A material balance study showed that little glucan (approx 10%) was solubilized as a result of the lime pretreatment, whereas about 26% of xylan and 29% of lignin became solubilized.

A combined RFLP-SSR-AFLP map of tetraploid cotton based on a Gossypium hirsutum x Gossypium barbadense backcross population

An interspecific Gossypium hirsutum x Gossypium barbadense backcross population of 75 BC1 plants was evaluated for 1014 markers. The map consists of 888 loci, including 465 AFLPs, 229 SSRs, 192 RFLPs, and 2 morphological markers, ordered in 37 linkage groups that represent most if not all of the 26 chromosomes, altogether spanning 4400 cM. Loci were not evenly distributed over linkage groups, and 18 of the 26 long groups had a single dense region. This paper proposes a partially revised list of the 13 pairs of homoeologous A/D chromosomes of the 2n = 4x = 52 tetraploid cotton genome. The major revisions, which involve the c3-c17, c4-c22, c5-D08, and c10-c20 homoeologous pairs, are based on the mapping of 68 SSR and RFLP loci with a known chromosome assignment, as well as on comparative alignments with previously published G. hirsutum x G. barbadense maps. The overall congruency in the locus orders and distances of common SSR and RFLP loci in these maps allows for an estimation of the consensus length that reaches a minimum of 5500 cM, and is encouraging for future efforts aimed at developing an integrated map of cultivated cotton. The present map also provides a firm framework for precision mapping of Mendelian components of quantitative traits in cotton

Commonly used antibacterial and antifungal agents for hospitalised paediatric patients: implications for therapy with an emphasis on clinical pharmacokinetics

Due to normal growth and development, hospitalised paediatric patients with infection require unique consideration of immune function and drug disposition. Specifically, antibacterial and antifungal pharmacokinetics are influenced by volume of distribution, drug binding and elimination, which are a reflection of changing extracellular fluid volume, quantity and quality of plasma proteins, and renal and hepatic function. However, there is a paucity of data in paediatric patients addressing these issues and many empiric treatment practices are based on adult data. The penicillins and cephalosporins continue to be a mainstay of therapy because of their broad spectrum of activity, clinical efficacy and favourable tolerability profile. These antibacterials rapidly reach peak serum concentrations and readily diffuse into body tissues. Good penetration into the cerebrospinal fluid (CSF) has made the third-generation cephalosporins the agents of choice for the treatment of bacterial meningitis. These drugs are excreted primarily by the kidney. The carbapenems are broad-spectrum beta-lactam antibacterials which can potentially replace combination regimens. Vancomycin is a glycopeptide antibacterial with gram-positive activity useful for the treatment of resistant infections, or for those patients allergic to penicillins and cephalosporins. Volume of distribution is affected by age, gender, and bodyweight. It diffuses well across serous membranes and inflamed meninges. Vancomycin is excreted by the kidneys and is not removed by dialysis. The aminoglycosides continue to serve a useful role in the treatment of gram-negative, enterococcal and mycobacterial infections. Their volume of distribution approximates extracellular space. These drugs are also excreted renally and are removed by haemodialysis. Passage across the blood-brain barrier is poor, even in the face of meningeal inflammation. Low pH found in abscess conditions impairs function. Toxicity needs to be considered. Macrolide antibacterials are frequently used in the treatment of respiratory infections. Parenteral erythromycin can cause phlebitis, which limits its use. Parenteral azithromycin is better tolerated but paediatric pharmacokinetic data are lacking. Clindamycin is frequently used when anaerobic infections are suspected. Good oral absorption makes it a good choice for step-down therapy in intra-abdominal and skeletal infections. The use of quinolones in paediatrics has been restricted and most information available is in cystic fibrosis patients. High oral bioavailability is also important for step-down therapy. Amphotericin B has been the cornerstone of antifungal treatment in hospitalised patients. Its metabolism is poorly understood. The half-life increases with time and can be as long as 15 days after prolonged therapy. Oral absorption is poor. The azole antifungals are being used increasingly. Fluconazole is well tolerated, with high bioavailability and good penetration into the CSF. Itraconazole has greater activity against aspergillus, blastomycosis, histoplasmosis and sporotrichosis, although it's pharmacological and toxicity profiles are not as favourable.

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.

International Rice Genome Sequencing Project: the effort to completely sequence the rice genome

The International Rice Genome Sequencing Project (IRGSP) involves researchers from ten countries who are working to completely and accurately sequence the rice genome within a short period. Sequencing uses a map-based clone-by-clone shotgun strategy; shared bacterial artificial chromosome/P1-derived artificial chromosome libraries have been constructed from Oryza sativa ssp. japonica variety 'Nipponbare'. End-sequencing, fingerprinting and marker-aided PCR screening are being used to make sequence-ready contigs. Annotated sequences are immediately released for public use and are made available with supplemental information at each IRGSP member's website. The IRGSP works to promote the development of rice and cereal genomics in addition to producing genome sequence data.

Simple inheritance of key traits distinguishing maize and teosinte

The segregation of key traits distinguishing maize and teosinte was analyzed in three F2 and three backcross populations derived from crosses of the modern maize inbred T232 with Zea mays ssp. parviglumis. These traits were (i) paired vs. single female spikelets; (ii) two-ranked vs. many-ranked ears; (iii) non-indurated vs. indurated glumes; (iv) inclination of the kernels toward the rachis, and (v) distichous vs. polystichous central staminate spike. All traits showed a simple mode of inheritance except for paired female spikes, which appeared to be controlled by two genes. The loci controlling these major changes were mapped with RFLP markers to four chromosomal regions. These results support the suggestion that maize became differentiated from teosinte with as few as five major gene changes.

The maize repressor-like gene intensifier1 shares homology with the r1/b1 multigene family of transcription factors and exhibits missplicing

The recessive mutation intensifier1 of maize apparently causes an overall increase in flavonoid production in the aleurone. The mechanism by which this is achieved is not understood. We have succeeded in cloning the intensifier1 gene by transposon tagging with Suppressor-mutator and found, by sequence analyses, that it shares homology with known transcription factors in the anthocyanin pathway, in particular the r1/b1 multigene family in maize. Two cDNAs and a genomic clone were completely sequenced, and together they showed that the transcripts were misspliced. The frequency of missplicing was investigated by polymerase chain reaction analyses and sequencing of the individual introns. These studies indicate that very little functional transcript was made. Indeed, missplicing may be a mechanism for reducing the levels of a transcription factor that, when present, acts as a repressor of anthocyanin biosynthesis.

Cloning and characterization of a maize cDNA encoding phytoene desaturase, an enzyme of the carotenoid biosynthetic pathway

To study regulation of the plastid-localized maize carotenoid biosynthetic pathway, a cDNA encoding phytoene desaturase (PDS) was isolated and characterized. The DNA sequence of the maize Pds cDNA was determined and compared with available dicot Pds genes. The deduced PDS protein, estimated at 64.1 kDa (unprocessed), had a dinucleotide binding domain and conserved regions characteristic of other carotene desaturases. Alignment of available PDS sequences from distantly related organisms suggests that Pds has potential as a phylogenetic tool. By use of heterologous complementation in Escherichia coli, maize PDS was shown to catalyze two desaturation steps converting phytoene to zeta-carotene. RFLP (restriction fragment length polymorphism) mapping was used to place Pds on chromosome 1S near viviparous5 (vp5), and RT-PCR (reverse-transcriptase polymerase chain reaction) analysis indicated reduced Pds transcript in vp5 mutant relative to normal endosperm. Other phytoene-accumulating mutant endosperms, vp2 and white3 (w3), showed no difference in Pds transcript accumulation as compared with normal endosperm counterparts. RT-PCR analysis of Pds transcript accumulation in developing endosperm showed Pds was constitutively expressed. Therefore, endosperm carotenogensis is not regulated by increasing the level of Pds transcripts.

Maize anthocyanin regulatory gene pl is a duplicate of c1 that functions in the plant

Genetic studies in maize have identified several regulatory genes that control the tissue-specific synthesis of purple anthocyanin pigments in the plant. c1 regulates pigmentation in the aleurone layer of the kernel, whereas pigmentation in the vegetative and floral tissues of the plant body depends on pl. c1 encodes a protein with the structural features of eukaryotic transcription factors and functions to control the accumulation of transcripts for the anthocyanin biosynthetic genes. Previous genetic and molecular observations have prompted the hypothesis that c1 and pl are functionally duplicate, in that they control the same set of anthocyanin structural genes but in distinct parts of the plant. Here, we show that this proposed functional similarity is reflected by DNA sequence homology between c1 and pl. Using a c1 DNA fragment as a hybridization probe, genomic and cDNA clones for pl were isolated. Comparison of pl and c1 cDNA sequences revealed that the genes encode proteins with 90% or more amino acid identity in the amino- and carboxyl-terminal domains that are known to be important for the regulatory function of the C1 protein. Consistent with the idea that the pl gene product also acts as a transcriptional activator is our finding that a functional pl allele is required for the transcription of at least three structural genes in the anthocyanin biosynthetic pathway.

Pinning down loose ends: mapping telomeres and factors affecting their length

A degenerately repeated sequence, proximal to the telomere heptanucleotide repeat in maize, contains restriction enzyme sites that permit the separation of telomeres from the rest of the chromosomes. Probing with a telomere-specific oligonucleotide revealed genotype-dependent telomere lengths that vary more than 25-fold in maize among the 22 inbreds that have been surveyed. These lengths were found to segregate reproducibly in a recombinant inbred family where 50% of the variation can be accounted for by three loci. The dynamic control over telomere length in maize appears to act rapidly to achieve new genotypically determined telomere lengths in the F1. Clones of telomere proximal sequences were used to map restriction fragment length loci at the distal ends of eight of 20 chromosome arms.

Changes in state of the Wx-m5 allele of maize are due to intragenic transposition of Ds

The molecular basis for the unusual phenotype conditioned by the waxy(Wx)-m5 Ds allele has been elucidated. Unlike most Ds alleles, Wx-m5 is phenotypically wild-type in the absence of Ac. We find that the Wx-m5 gene contains a 2-kb Ds element at -470 relative to the start of Wx transcription, representing the most 5' insertion of any transposable element allele characterized to date in plants. Despite its wild type phenotype, Wx-m5 has reduced levels of Wx enzymatic activity indicating that Ds insertion influences Wx gene expression. In the presence of Ac, Wx-m5 kernels have sectors of null expression on a wild-type background and give rise to stable wx and unstable wx-m germinal derivatives. Seventeen of 20 derivatives examined are wx-m alleles and at least 15 of these appear to result from intragenic transposition of Ds from -470 to new sites within the Wx gene. Three wx-m alleles contain two Ds elements, one at -470 and a second in Wx coding sequences. Surprisingly, only 3 out of 20 derivatives are stable wx mutants and these have sustained gross rearrangements of Wx and flanking sequences. For most other maize transposable element alleles somatic sectors and germinal derivatives usually arise following element excision or deletions of element sequences. In contrast, element insertion following intragenic transposition is apparently responsible for most of the somatic sectors and germinal derivatives of Wx-m5.

Recombinant inbreds for molecular mapping in maize: theoretical and practical considerations

Molecular mapping is rapidly being extended to more species as one result of the current emphasis on genome initiatives. The choice of the population used for mapping can have important consequences on the efficiency and accessibility of the mapping information. Recombinant inbred lines offer certain advantages over other mapping populations for many species. These more or less permanent populations permit many geneticists to contribute to the mapping effort and to profit from each other's work. Recombinant inbred lines are used extensively in mouse genetics and have been used in maize to compile a detailed molecular map.

An arginine to lysine substitution in the bZIP domain of an opaque-2 mutant in maize abolishes specific DNA binding

The opaque-2 (o2) locus in maize encodes a transcription factor involved in the regulation of zein storage proteins. We have shown previously that the O2 protein contains a leucine zipper domain that binds to promoters of 22-kD zein genes. In this paper we characterize an EMS-induced o2 allele, o2-676, that causes a 50% reduction in zein. We have found that the o2-676 mutant protein does not show specific recognition of zein promoter fragments because of the substitution of a lysine residue for an arginine residue within the bZIP domain of o2-676. This particular arginine is conserved within the bZIP domains of all mammalian, fungal, and plant DNA binding proteins of this class. The correlation between this mutation in o2 and the altered pattern of zein expression strongly suggests that O2 regulates transcription of certain members of the zein multigene family through direct interaction with the zein promoters and not through the transcriptional activation of some other regulator of zein gene expression.

Maize regulatory gene opaque-2 encodes a protein with a "leucine-zipper" motif that binds to zein DNA

The opaque-2 locus (o2) in maize regulates the expression of many members of the zein multigene family of storage proteins. cDNA clones for a wild-type allele of the (o2) locus (O2) were isolated from a maize endosperm cDNA library and sequenced. We found a 258-nucleotide 5' leader sequence containing three short open reading frames followed by a sequence specifying a protein of 437 amino acids. The presumptive amino acid sequence of the protein (O2) specified by the O2 cDNA contains a "leucine-zipper" domain characteristic of some mammalian and fungal transcription activation factors. lacZ-O2 fusion constructs, using nearly the entire coding region of O2 or only a fragment specifying the leucine-zipper domain, were expressed in Escherichia coli. In an in vitro binding assay, the beta-galactosidase-O2 fusion proteins bound to two specific regions on the 5' side of the coding sequence in a zein genomic clone. This suggests that the O2 protein affects zein transcription through direct interaction with one or more zein promoter elements.

cDNAs of two non-allelic sucrose synthase genes in maize: cloning, expression, characterization and molecular mapping of the sucrose synthase-2 gene

cDNA clones of the two non-allelic sucrose synthase (Ss) genes, Ss2 and Sh, have been isolated from λgt11 expression libraries derived from immature kernel poly(A)(+) RNA of sh-deletion and Sh/Sh genotypes of maize respectively. Recombinant clones containing the longest Ss2 and Sh cDNA inserts, each of approximately 2.5 kb size, were characterized and comparatively analyzed. Although the Sh cDNA insert expresses as a sucrose synthase-1 (SS1) β-galactosidase fusion protein (∼ 200 kD) in λ lysogens, the Ss2 cDNA failed to form such a chimeric protein and instead showed a ∼ 70 kD SS2 polypeptide. The Ss2 and Sh cDNAs as hybridization probes on RNA blots of immature kernels detected a larger Ss2 transcript (∼ 2900 b) than the Sh transcript (∼ 2750 b). Because SS1 and SS2 protein subunits are known to be of identical size, the significance of difference in transcript size is not apparent. A comparative restriction enzyme mapping of the two cDNA clones and a genomic Ss2 clone show sequence diversity over the entire lengths of Ss2 and Sh clones. Interestingly, restriction endonuclease sites around the 3' ends are more conserved than the 5' ends of these two genes. Genetic data indicate that the Ss2 locus is on chromosome 9 and molecular mapping using the Ss2 cDNA clone on recombinant inbred lines and B-A translocations stocks suggest that Ss2 is about 20 map units away from the Wx locus on 9L.

Gene mapping with recombinant inbreds in maize

Recombinant inbred lines of maize have been developed for the rapid mapping of molecular probes to chromosomal location. Two recombinant inbred families have been constructed from F2 populations of T232 X CM37 and CO159 X Tx303. A genetic map based largely on isozymes and restriction fragment length polymorphisms has been produced that covers virtually the entire maize genome. In order to map a new gene, an investigator has only to determine its allelic distribution among the recombinant inbred lines and then compare it by computer with the distributions of all previously mapped loci. The availability of the recombinant inbreds and the associated data base constitute an efficient means of mapping new molecular markers in maize.

Advantages and limitations of using Spm as a transposon tag

Transposon tagging has become the method of choice for isolating genes whose products are in low abundance. We have recently used the transposable element Spm to tag and clone maize regulatory loci. Our choice of Spm was dictated by several factors: The frequency of transposition of Spm is high enough to obtain detectable transposition events, into loci affecting kernel traits, in populations of less than 10(6) seed. Although the copy number of Spm is high in the maize genome, insertions into the gene of interest can be distinguished from other Spm copies by digesting DNAs from segregating populations with methyl-sensitive restriction enzymes, and hybridizing with Spm-specific probes. Since all members of the Spm family thus far examined share DNA homology, hybridization with appropriate probes allows detection of insertions of both autonomous and defective elements. Thus, if a mutable allele can be shown to be under Spm control, one can be reasonably confident of successfully cloning that allele.

Activation of silent transposable elements

It is well known among maize geneticists that agents that cause chromosome breakage can activate quiescent transposable elements. However, other than temporarily relieving position effect, it is difficult to understand how these events can lead directly to activation. One possibility is that chromosome breakage can initiate a process in the cell resulting in a higher rate of spontaneous mutation. Such a system could be analogous to the SOS response of Escherichia coli in which an error-prone repair system is induced. Chemical mutagens that cause little chromosome breakage but add bulky adducts to the DNA can induce the SOS response. In seed homozygous for a1-m2(8004), wx-m8, no active Spm, that had been treated with ethyl methanesulfonate, we observed activation of Spm at the rate of 1.1 x 10(-4). The spontaneous rate of activation in this material was 1.2 x 10(-5). Most of the activation events occurred as single kernels. This result contrasts with sectors covering at least one-eighth of the ear that would have been expected if activation had occurred as a direct result of mutagenesis in the mature kernel. The late timing of these events suggests that the activation, in most instances, may not be the direct result of chemical mutagenesis.

Transposon tagging and molecular analysis of the maize regulatory locus opaque-2

Genetic analyses suggested that the opaque-2 (o2) locus in maize acts as a positive, transacting, transcriptional activator of the zein seed storage-protein genes. Because isolation of the gene is requisite to understanding the molecular details of this regulation, transposon mutagenesis with the transposable element suppressor-mutator (Spm) was carried out, and three mutable o2 alleles were obtained. One of these alleles contained an 8.3-kilobase autonomous Spm, another a 6.8-kilobase nonautonomous Spm, and the third an unidentified transposon that is unrelated to Spm. A DNA sequence flanking the autonomous Spm insertion was verified to be o2-specific and provided a probe to clone a wild-type allele. Northern blots indicated that the gene is expressed in wild-type endosperm but not in leaf tissues or in endosperms homozygous for a mutant allele of the O2 gene. A transcript was detected in endosperms homozygous for mutations at opaque-7 and floury-2, an indication that O2 expression is independent of these two other putative regulators of zein synthesis.

DNase I hypersensitivity and expression of the Shrunken-1 gene of maize

The local chromatin structure of the Shrunken-1 (Sh) gene of maize was probed by analyzing DNase I hypersensitivity. Sh encodes the gene for sucrose synthetase, a major starch biosynthetic enzyme, which is maximally expressed in the endosperm during seed maturation. In addition to general DNase I sensitivity, specific DNase I hypersensitive sites were identified in endosperm chromatin that mapped near the 5' end of the Sh gene. The pattern of hypersensitive sites and their relative sensitivity were altered in other non-dormant tissues that produce little or no enzyme. However, some changes in chromatin structure appear to be independent of Sh gene expression and may reflect general alterations associated with plant development. The chromatin structure of several sh mutations, induced by Ds controlling element insertions, was also analyzed. Although the insertions perturbed expression of the gene, there were no notable effects on local chromatin structure.

Molecular analysis of the maize anthocyanin regulatory locus C1

The C1 gene of maize plays a regulatory role in the production of anthocyanin pigments in the aleurone layer of the endosperm. As an initial step toward understanding the molecular details of how C1 controls pigment biosynthesis, we cloned the C1 gene. This was accomplished by first cloning a mutable allele of C1, c1-m5, which contains the transposable element Spm. A combination of molecular and genetic analysis was used to identify the Spm at the C1 locus. Individual genomic DNAs from a population in which the c1-mutable phenotype was segregating with the recessive c1 phenotype were digested with methyl-sensitive restriction enzymes and probed with a small DNA fragment derived from a defective Spm. One Sal I restriction fragment complementary to the Spm probe was shown to be present in the DNA of individuals with the c1-m5 phenotype but absent from DNA of individuals with a recessive c1 phenotype. Subsequent cloning and restriction analysis of this fragment revealed sequences flanking the Spm that proved to be C1-specific. A DNA fragment derived from the flanking sequences was then used as a probe to clone the wild-type C1 gene and several additional alleles of C1, including one stable recessive, two mutations caused by Ds insertions, one mutation induced by insertion of a defective Spm, and two dominant mutations, C1-S and C1-I. RNA blot hybridization analysis of three C1 alleles indicates that C1 regulation of the Bz1 and A1 structural genes in the anthocyanin biosynthetic pathway is at the transcriptional level.

The suitability of restriction fragment length polymorphisms as genetic markers in maize

Strain identification in Zea mays by restriction fragment length polymorphism should be feasible due to the high degree of polymorphism found at many loci. The polymorphism in maize is apparently higher than that currently known for any other organism. Five randomly selected maize inbred lines were examined by Southern filter hybridization with probes of cloned low copy sequences. Typically, several alleles could be distinguished among the inbred lines with any one probe and an appropriately selected restriction enzyme. Despite considerable polymorphism at the DNA level, 16 RFLP markers in three inbred lines of maize were examined for six to 11 generations and found be stable. Mapping of RFLP markers in maize can be accelerated by the use of B-A translocation stocks, which enable localization of a marker to chromosome arm in one generation. The use of recombinant inbred lines in further refinement of the map is discussed.

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.

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.

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.

CONTROLLING-ELEMENT EVENTS AT THE SHRUNKEN LOCUS IN MAIZE

We have examined insertions of the controlling element Ds at the Shrunken locus of maize. A cDNA probe complementary to a portion of the Shrunken locus mRNA was prepared. This probe recognizes a unique sequence in maize DNA. Using lines carrying derivatives of the same short arm of chromosome 9, we have detected modifications at the nucleic acid level caused by Ds. The changes appear to be large insertions, one of which may be more than 20 kilobase pairs in length. These observations provide a basis for the isolation and molecular characterization of one of the maize controlling elements.

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.

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.

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.

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.)