Eel electric organ: hyperexpressing calmodulin system.

The electroplax of the electric eel Electrophorus electricus is the most abundant source of the calcium-binding protein calmodulin. The electroplax has 250 times the amount of calmodulin and its mRNA than eel skeletal muscle. Our data suggest that there is no major difference in gene copies, the degree of methylation, or genome rearrangement of the calmodulin gene in DNAs from eel electroplax and muscle. Differences in the calmodulin-binding proteins in electroplax and muscle suggest a differential role for the functional expression of calmodulin in cellular regulation.     

Texture discrimination by Gabor functions

A 2D Gabor filter can be realized as a sinusoidal plane wave of some frequency and orientation within a two dimensional Gaussian envelope. Its spatial extent, frequency and orientation preferences as well as bandwidths are easily controlled by the parameters used in generating the filters. However, there is an uncertainty relation associated with linear filters which limits the resolution simultaneously attainable in space and frequency. Daugman (1985) has determined that 2D Gabor filters are members of a class of functions achieving optimal joint resolution in the 2D space and 2D frequency domains. They have also been found to be a good model for two dimensional receptive fields of simple cells in the striate cortex (Jones 1985; Jones et al. 1985).The characteristic of optimal joint resolution in both space and frequency suggests that these filters are appropriate operators for tasks requiring simultaneous measurement in these domains. Texture discrimination is such a task. Computer application of a set of Gabor filters to a variety of textures found to be preattentively discriminable produces results in which differently textured regions are distinguished by firstorder differences in the values measured by the filters. This ability to reduce the statistical complexity distinguishing differently textured region as well as the sensitivity of these filters to certain types of local features suggest that Gabor functions can act as detectors of certain texton types. The performance of the computer models suggests that cortical neurons with Gabor like receptive fields may be involved in preattentive texture discrimination.     

Systematic study ofOsbertia (Asteraceae-Astereae)

Osbertia, a stoloniferous group confined to the montane regions of Mexico and adjacent Guatemala, was first proposed as a genus byGreene (1895), but most workers have retained the taxon as part ofHaplopappus. It is clearly closer toNoticastrum, Erigeron orHeterotheca than it is toHaplopappus sensu stricto. The present treatment recognizes two species, a widespread highly variableOsbertia stolonifera and a newly describedO. chihuahuana from northwestern Mexico. Distribution maps, distinguishing features, full synonymy and illustrations are presented.     

Transformation of Aspergillus nidulans by the orotidine-5'-phosphate decarboxylase gene of Neurospora crassa

Relief of an auxotrophic requirement for uridine in Aspergillus nidulans strain G191 has been achieved by transformation with a segment of Neurospora crassa DNA containing the corresponding gene coding for orotidine-5'-phosphate decarboxylase. The mitotic stability of such transformants suggests that the DNA has integrated into the genome. Southern hybridisation analysis of DNA isolated from transformants revealed the presence of pBR322 sequences which have integrated into the host genome along with the N. crassa DNA.     

Role of pit membranes in macromolecule-induced wilt of plants

Macromolecules present in low concentrations in xylem fluid of Medicago sativa L. var DuPuits will increase the resistance to xylem liquid flow. This increase in resistance was found to be reversible by backflushing the xylem. Autoradiography showed that very large molecules do not pass through pit membrane pores. A comparison of pit membrane pore sizes to molecule sizes suggests that increased resistance to xylem flow is a result of plugging pit membrane pores. It was also found that pit membranes located in two parts of the plant differ in the apparent diameter of their pores and, thus, in their susceptibility to plugging by macromolecules. Macromolecules in xylem fluid may result from hostparasite interactions and may play a significant role in the outcome of the interaction.     

Identification of sites of 4'-(hydroxymethyl)-4,5',8-trimethylpsoralen cross-linking in Escherichia coli 23S ribosomal ribonucleic acid

The reagent 4'-(hydroxymethyl)-4,5',8-trimethylpsoralen (HMT) was used to cross-link 23S rRNA from Escherichia coli under 50S ribosomal subunit reconstitution conditions. Following partial digestion of the RNA with ribonuclease T1, two-dimensional diagonal electrophoresis in denaturing polyacrylamide gels was used to isolate fragments derived from the cross-linked sites. These fragments were analyzed by digestion with ribonucleases T1 and A and their positions in the 23S RNA sequence identified. Fragment a1 (positions 1325-1426) is cross-linked to a2 (positions 1574-1623); fragment b1 (positions 1700-1731) is cross-linked to b2 (positions 1732-1753); and a cross-link is formed within fragment c (or c') (positions 863-916). In the latter case, the cross-link was located precisely, linking residues C867 and U913. All three HMT-mediated cross-links are consistent with a proposed secondary structure model for 23S RNA [Noller, H. F., Kop, J., Wheaton, V., Brosius, J., Gutell, R. R., Kopylov, A. M., Dohme, F., Herr, W., Stahl, D. A., Gupta, R., & Woese, C. R. (1981) Nucleic Acids Res. 9, 6167-6189].     

Comparative analysis of the 5''-end regions of two repressible acid phosphatase genes in Saccharomyces cerevisiae.

The nucleotide sequence of 5'-noncoding and N-terminal coding regions of two coordinately regulated, repressible acid phosphatase genes from Saccharomyces cerevisiae were determined. These unlinked genes encode different, but structurally related polypeptides of molecular weights 60,000 and 56,000. The DNA sequences of their 5'-flanking regions show stretches of extensive homology upstream of, and surrounding, a "TATA" sequence and in a region in which heterogeneous 5' ends of the p60 mRNA were mapped. The predicted amino acid sequences encoded by the N-terminal regions of both genes were confirmed by determination of the amino acid sequence of the native exocellular acid phosphatase and the partial sequence of the presecretory polypeptide synthesized in a cell-free protein synthesizing system. The N-terminal region of the p60 polypeptide was shown to be characterized by a hydrophobic 17-amino acid signal polypeptide which is absent in the native exocellular protein and thought to be necessary for acid phosphatase secretion.     

Histone gene number and organisation in Xenopus: Xenopus borealis has a homogeneous major cluster

Using a Xenopus laevis H4 cDNA clone as a probe we have determined that the numbers of H4 histone genes in Xenopus laevis and Xenopus borealis are approximately the same. These numbers are dependent on the hybridization stringency and we measure about 90 H4 genes per haploid genome after a 60 degrees C wash in 3 X SSC. Using histone probes from both Xenopus and sea urchin we have studied the genomic organization of histone genes in these two species. In all of the X.borealis individuals analyzed about 70% of the histone genes were present in a very homogeneous major cluster. These genes are present in the order H1, H2B, H2A, H4 and H3, and the minimum length of the repeated unit is 16kb. In contrast, the histone gene clusters in X.laevis showed considerable sequence variation. However two major cluster types with different gene orders seem to be present in most individuals. The differences in histone gene organization seen in species of Xenopus suggest that even in closely related vertebrates the major histone gene clusters are quite fluid structures in evolutionary terms.