Nucleotide sequence of the split tRNAleu(UAA) gene from Sorghum bicolor chloroplasts

The nucleotide (nt) sequence of the split tRNAleu(UAA) gene and 328 nt of its flanking regions from sorghum chloroplasts (cp) has been determined. This gene is located in the BamHI-6 fragment in a map position very similar to that of maize. The exon of sorghum tRNAleu gene has an identical nt sequence to its counterpart in maize. Although the 450 nt of intron in sorghum is 8 nt shorter than that of maize, the nt sequence between them shows 97% homology. Like maize and broad bean, the intron from sorghum cp tRNAleu gene could be folded into a secondary structure which is similar to the postulated structure of the intron from the auto-spliceable rRNA precursor of Tetrahymena. Both introns from sorghum and maize contain open reading frames (ORFs) which are conserved at the N terminus. The putative AUG initiation codon for both ORFs is located in the stem region of a 12-bp secondary structure of highly A + T-rich sequences.     

Evolution of the ATP-binding-cassette transmembrane transporters of vertebrates

The ATP-binding-cassette transmembrane transporters (ABC transporters) known from vertebrates belong to four major subfamilies: (1) the P- glycoproteins (Pgp); (2) the cystic fibrosis transmembrane conductance regulators (CFTR); (3) the Tap proteins encoded with the major histocompatibility complex of mammals; and (4) the peroxisomal membrane proteins. Both Pgp and CFTR have a structure suggesting a past internal gene duplication; a phylogenetic analysis indicated that these duplications occurred independently, while an independent tandem gene duplication occurred in the case of the Tap family. Both the Pgp and Tap proteins show evidence of relationship to bacterial ABC transporters lacking internal duplication, and both are significantly more closely related to the HlyB and MsbA families of transporters from purple bacteria than they are to ABC transporters from nonpurple bacteria. The simplest hypothesis to explain this observation is that eukaryotic Pgp and Tap genes are descended from a mitochondrial gene or genes that were subsequently translocated to the nuclear genome. The Pgp genes of eukaryotes are characterized by a remarkable degree of convergent evolution between the ATP-binding cassettes of their N- terminal and C-terminal halves, whereas no such convergence is seen between the two halves of CFTR genes or between the duplicated Tap genes. Exon 13 of the CFTR gene, which encodes a putative regulatory domain not found in other ABC transporters apart from CFTR, showed high levels of both synonymous and nonsynonymous difference in comparisons among different mammalian species, suggesting that this region is a mutational hot spot.      

CHLOROPLAST DNA VARIATION AND THE PHYLOGENY OF HORDEUM (POACEAE)

Restriction site variation in the chloroplast genome (cpDNA) was surveyed among 37 taxa or cytotypes (40 accessions) of the genus Hordeum. Seventeen restriction enzymes were employed, and a total of 491 restriction sites were assayed. Of these, 120 were variable among the taxa, including 70 synapomorphies. The level of sequence divergence (p) among species of Hordeum varied from 0.0 to 0.017, indicating that Hordeum possesses an about-average level of cpDNA diversity as compared to most other genera of flowering plants for which data are available. Wagner and polymorphism parsimony phytogenies were constructed from the restriction site data. These analyses divided the genus into several distinct groups; 1) American taxa; 2) diploid H. marinum; 3) Asian taxa; 4) H. vulgare-H. bulbosum; and 5) the H. murinum complex. Bootstrap-based confidence limits provided statistical support for the monophylesis of the latter three groups. The cpDNA data showed remarkably good congruence with previously published isoenzymatic, molecular, cytological, and crossing data.     

Evidence for the presence of β-lactamase inStreptomyces glaucescens and its inhibition by sodium clavulanate

Streptomyces glaucescens is shown to possess -lactamase activity which is inhibitable by clavulanate. This is important in regard to its use as a cloning host for enzymes of \-lactam biosynthesis.     

Teosinte Branched1 and the Origin of Maize: Evidence for Epistasis and the Evolution of Dominance

Two quantitative trait loci (QTL) controlling differences in plant and inflorescence architecture between maize and its progenitor (teosinte) were analyzed. Complementation tests indicate that one of these, which is on chromosome arm 1L, is the locus for the maize mutant teosinte branched1 (tb1). This QTL has effects on inflorescence sex and the number and length of internodes in the lateral branches and inflorescences. This QTL has strong phenotypic effects in teosinte background but reduced effects in maize background. The second QTL, which is on chromosome arm 3L, affects the same traits as the QTL on 1L. We identify two candidate loci for this QTL. The effects of this QTL on several traits are reduced in both maize and teosinte background as compared to a maize-teosinte F(2) population. Genetic background appears to affect gene action for both QTL. Analysis of a population in which both QTL were segregating revealed that they interact epistatically. Together, these two QTL substantially transform both plant and inflorescence architecture. We propose that tb1 is involved in the teosinte plant's response to local environment to produce either long or short branches and that maize evolution involved a change at this locus to produce short branches under all environments.     

Genetic Analysis of the Morphological Differences between Maize and Teosinte

Molecular marker loci were used to investigate the inheritance of morphological traits that distinguish maize (Zea mays ssp. mays) from a closely related wild relative, teosinte (Z. mays ssp. mexicana). Regression and interval mapping analyses gave largely congruent results concerning the numbers of loci controlling the morphological traits and the magnitudes of their effects; however, interval mapping tended to give larger estimates for the magnitudes of the effects of the morphological trait loci. This tendency was exaggerated for traits that were non-normally distributed. Variation for most inflorescence traits is controlled by one or two regions of the genome with large effects plus several other regions with relatively small effects. As such, the data are congruent with a mode of inheritance for most traits involving one or two major loci plus several minor loci. Regions of the genome with large effects on one trait consistently had smaller effects on several other traits, possibly as a result of pleiotropy. Most of the variation for the dramatic differences in inflorescence morphology between maize and teosinte is explained by five restricted regions of the genome. One of these regions encompasses a previously described gene, tb1 (teosinte branched), and the effects of this region on inflorescence architecture are similar to the known effects of tb1. Implications of this work for the genetic basis of morphological evolution in plants are discussed.     

Mapping the genes that made maize.

George Beadle proposed that the striking morphological differences between cultivated maize and its probable wild progenitor (teosinte) were initiated by a small number of mutations with large effects on adult morphology. Recent genetic analyses using molecular markers provide some support for this view and show where in the maize genome the putative loci are likely to be located. This work sets the stage for fine-scale linkage mapping of these genomic regions and the eventual cloning of the genes involved in this remarkable evolutionary transformation.     

Three-Dimensional Trabecular Alignment Model

The Shear-slip Mesh Update Method (SSMUM) is being used in flow simulations involving large but regular displacements of one or more boundaries of the computational domain. We follow up the earlier discussion of the method with notes on practical implementation aspects. In order to establish a benchmark problem for this class of flow problems, we define and report results from a two-dimensional viscous flow around a rotating stirrer in a square chamber. The application potential of the method is demonstrated in the context of biomedical design problem, as we perform an analysis of blood flow in a centrifugal left ventricular assist device, or blood pump, which involves a rotating impeller in a non-axisymmetric housing.