Intranuclear complexes in a copper-tolerant green alga

The results of ultrastructural studies and transmission electron microscope microanalysis of two Scenedesmus strains experimentally exposed to copper sulfate are presented. A fine-structural examination of the cells revealed the presence of nuclear inclusions in the form of central dense-core complexes. Cytoplasmic structures resembling the intranuclear inclusions were occasionally found in the cells. TEM-X-ray microanalysis of these structures has provided evidence that the inclusions contain copper. It is concluded that their presence may be regarded as a detoxifying mechanism.     

Characteristics of inheritance of restriction fragment polymorphisms for non-transcribed spacers of human rRNA genes

Inheritance of polymorphous restricts of nontranscribed spacer (NTS) located to the right from 3'-end of 28S rRNA gene has been studied in families. Single classes of NTS polymorphous fragments are presented in the genome by some tenths of copies and are inherited as a simple mendelian characteristic located on separate chromosomes.     

Phylogeny of Cucurbitaceae species in Korea based on 5S rDNA non-transcribed spacer

The 5S rDNA coding region and its spacer have been successfully utilized in phylogenetic studies of plants. However, it has not been utilized in the phylogenetic analysis of Cucurbitaceae. Here, we obtained the 5S rDNA sequences of 12 Cucurbitaceae species by direct PCR or cloning. The 5S rDNA sequences ranged from 275 to 359 bp, and the coding regions of all species were 120 bp long, except for that of Cucurbita, which was 119 bp. Some genus-specific SNPs were observed in the coding regions of Cucurbita, Lagenaria, Melothria, and Tricosanthes. The GC content of the coding regions was generally higher than that of the NTS regions, and the difference in GC content between the coding and NTS regions varied among species, with Gynostemma pentaphyllum having the greatest difference of 20.3. The phylogenetic trees generated using maximum parsimony and maximum likelihood were congruent and well supported by the recently published classification of Cucurbitaceae. These results demonstrated the utility of the 5S rDNA sequence in inferring phylogenetic relationships among 12 Cucurbitaceae species, and its utility could be extended by using a greater number of species in future studies.     

Structural organization of mouse rDNA: Comparison of transcribed and non-transcribed regions

Summary The DNA of the recombinant phage gtWES Mr974 (Grummt et al., 1979) which contains the 18S region and adjacent spacer sequences of the ribosomal genes from mouse has been digested with the restriction endonuclease Sall. Fragments corresponding to the non-transcribed spacer (A and D) and the external transcribed spacer (B) have been prepared and their nucleotide composition and sequence organization has been determined. The data indicate that the part of the non-transcribed spacer contained in Mr974 consists of at least two structural domains of distinct sequence characteristics. Fragment A contains 49% G+C and exhibits a high sequence complexity. Fragment D, the spacer fragment flanking the coding region, is very rich in G+C and is obviously composed of an internally repetitive sequence which is cut by several restriction enzymes into a similar set of repetitive fragments. Most of the fragments have sizes that are multiples of 60 and 80 or 140 base pairs, respectively, suggesting an alternating 60/80bp arrangement. This regular sequence in fragment D accounts both for the observed instability and length heterogeneity of the rDNA insert in several clones and probably for the heterogeneity in the structure of the ribosomal repeats in the genomic DNA.     

microRNAs in a multicellular green alga Volvox carteri

microRNAs(miRNAs)have emerged as key components in the eukaryotic gene regulatory network.We and others have previously identified many miRNAs in a unicellular green alga,Chlamydomonas reinhardtii.To investigate whether miRNA-mediated gene regulation is a general mechanism in green algae and how miRNAs have been evolved in the green algal lineage,we examined small RNAs in Volvox carteri,a multicellular species in the same family with Chlamydomonas reinhardtii.We identified 174 miRNAs in Volvox,with many of them being highly enriched in gonidia or somatic cells.The targets of the miRNAs were predicted and many of them were subjected to miRNA-mediated cleavage in vivo,suggesting that miRNAs play regulatory roles in the biology of green algae.Our catalog of miRNAs and their targets provides a resource for further studies on the evolution,biological functions,and genomic properties of miRNAs in green algae.     

Site-specific initiation of DNA replication within the non-transcribed spacer of Physarum rDNA.

Physarum polycephalum rRNA genes are found on extrachromosomal 60 kb linear palindromic DNA molecules. Previous work using electron microscope visualization suggested that these molecules are duplicated from one of four potential replication origins located in the 24 kb central non-transcribed spacer [Vogt and Braun (1977) Eur. J. Biochem., 80, 557-566]. Considering the controversy on the nature of the replication origins in eukaryotic cells, where both site-specific or delocalized initiations have been described, we study here Physarum rDNA replication by two dimensional agarose gel electrophoresis and compare the results to those obtained by electron microscopy. Without the need of cell treatment or enrichment in replication intermediates, we detect hybridization signals corresponding to replicating rDNA fragments throughout the cell cycle, confirming that the synthesis of rDNA molecules is not under the control of S-phase. The patterns of replication intermediates along rDNA minichromosomes are consistent with the existence of four site-specific replication origins, whose localization in the central non-transcribed spacer is in agreement with the electron microscope mapping. It is also shown that, on a few molecules, at least two origins are active simultaneously.     

An actin-like protein and gene in the unicellular green alga Dunaliella

We present evidence for an actin-like protein in the unicellular alga Dunaliella (Volvocales) which has a molecular weight comparable to that of vertebrate skeletal muscle actin. Intracellular detection using indirect immunofluorescence indicates that this protein is present in the cytoplasm. Using mouse actin c-DNA probes, we show that this protein is probably encoded by a single gene in the Dunaliella genome.     

Three photosynthetic antenna porphyrins in a primitive green alga

Fluorescence excitation spectra (between 400–500 and 610–700 nm) for chlorophyll emission from particles and detergent extracts of the primitive green microalga, Mantoniella, were measured. The results showed that the prophyrin, magnesium 2,4-divinylpheoporphyrin a₅, which this alga accumulates in addition to Chl b, also can transfer excitation energy to Chl a, and therefore act as antenna for photosynthesis. Evidence was found that magnesium 2,4-divinylpheoporphyrin a₅ has a Soret band near 450 nm in vivo which further increases the light-harvesting capacity of these algae growing deep in the open ocean.     

Nitrogen fixation associated with a hotspring green alga

A unicellular alga which can grow in the light without a combined nitrogen source was isolated from a hot spring. The cells were almost spherical, usually 5–10 m in diameter. Absorption spectra of the watersoluble pigments and of the acetone-extracted ones revealed the existence of chlorophyll a and b and the absence of phycobilins. Thin sections examined by electron microscopy revealed an eukaryotic organization with features typical of the coccoid green algae (the Chlorococcales). Cells divided by internal cytokinesis and subsequent liberation of daughter cells from the parental wall, in a way similar to Chlorella. The alga reduced acetylene to ethylene and incorporated ¹⁵N₂ into cell protoplasm when incubated in a low oxygen atmosphere. Nitrogenase activity was light-dependent, microaerophilic and thermophilic. Although the association of symbiotic nitrogen fixing prokaryotes with the cells may still be possible, any such organisms have not so far been detected.Abbreviations Used DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - Chl chlorophyll - MBM modified Bristol medium - TLC thin layer chromatography     

An anticoagulant proteoglycan from the marine green alga, Codium pugniformis

An anticoagulant isolated from the marine green alga Codium pugniformis was composed mainly of glucose with minor amounts of arabinose and galactose. It was highly sulfated (326 μg mg^-1 polysaccharide) and contained protein(52 μg mg^-1 polysaccharide) and was thus a proteoglycan. The anticoagulant properties of the purified proteoglycan were compared with those of heparin by studying the activated partial thromboplastin time (APTT), prothrombin time (PT) and thrombin time(TT) using normal human plasma. The proteoglycan showed similar activities to heparin, but was weaker than heparin. On the other hand, the proteoglycan did not affect PT even at the concentration at which APTT and TT were prolonged. The anticoagulation mechanism of this proteoglycan was due to the direct inhibition of thrombin and the potentiation of antithrombin III. This revised version was published online in August 2006 with corrections to the Cover Date.     

Detectability, movements and apparent lack of homing in

Translocation is an important tool in the conservation of New Zealand reptiles. Despite this, it is generally not known how Hoplodactylus geckos respond to being translocated, partly because they are difficult to monitor. In this opportunistic study, common geckos (H. maculatus) were captured from a site at Birdlings Flat (South Island, New Zealand) that was destined for destruction, and released in native coastal shrubland km away. Geckos were sampled monthly using pitfall traps and artificial retreats, with only the latter method yielding captures. Ten out of translocated geckos remained at the release site, and translocated animals moved equivalent distances to resident geckos (n = 3) over a -year period following translocation. Although studies spanning multiple decades may be needed to determine whether translocations of Hoplodactylus geckos are ultimately successful given their life-history traits, the development of an effective detection method is nonetheless a useful contribution.