A NEW GENUS OF PROTOSTELIDS SHOWING AFFINITIES WITH CERATIOMYXA

A new genus and species of the Protosteliida (Mycetozoa), Ceratiomyxella tahitiensis, was isolated from dead plant material—var. tahitiensis from Tahiti and var. neotropicalis from Brazil and Colombia. The sporocarps have deciduous spores borne singly on slender hollow stalks; zoocysts with anteriorly flagellate planonts are produced. The trophic stage is comprised of uninucleate to plurinucleate amoeboid cells and reticulate plasmodia; the uninucleate cells become flagellate in water. The prespore cells and spores are plurinucleate. Sexuality has not been demonstrated. Var. tahitiensis has globose spores and produces its zoocysts just after spore germination, whereas var. neotropicalis has subglobose spores and forms zoocysts later in the life cycle. The species is thought to show phylogenetic relationships with Ceratiomyxa, which was recently transferred to the Protosteliida by Olive.     

MONOGRAPH OF THE GENUS PROTOSTELIUM

Three new species of Protostelium (Order Protostelida of the Mycetozoa) are described: P. irregularis, P. zonatura, and P. pyriformis, all with rather wide distribution and occurring on dead attached plant parts, less often in soil and humus. The latter two species differ from the first and from the other two known species, P. mycophaga Olive and Stoianovitch and P. arachisporum Olive, in the endogenous origin of the stalk. P. mycophaga var. crassipes, with vesicular stalk bases, is the third variety of that species to be described. A key to the genus is included.     

Functional properties of the anaerobic responsive element of the maize Adh1 gene

The functional properties of the anaerobic responsive element (ARE) of the maize Adh1 gene have been analysed using a transient expression assay in electroporated maize protoplasts. The ARE functions in both orientations although inversion of the ARE sequence relative to the TATA box element produces slightly weaker promoter activity under anaerobic conditions and elevated expression under aerobic conditions. Promoter activity under anaerobic conditions is proportional to the number of complete ARE sequences in the Adh1 promotor. The ARE contains two sub-regions and dimers of sub-region II are as efficient as the wild-type sequence in activating gene expression under anaerobic conditions. However, sub-region I dimers do not appear capable of inducing gene expression in response to anaerobic stress. We conclude that sub-region II is essential for anaerobic induction of gene expression. Reporter gene expression remains constant when the spacing between sub-regions of the ARE is increased up to at least 64 bp, but increased spacing of 136 bp or greater abolishes expression in both aerobic and anaerobic conditions, indicating that a close association of the two sub-regions is required both for anaerobic responsiveness and for maximal levels of aerobic gene expression. When the ARE is placed upstream of position –90 of the CaMV 35S promoter, the ARE produces a high level of expression in both aerobic and anaerobic conditions. The general enhancement of gene expression driven by the hybrid ARE/35S promoter in aerobic conditions requires an intact sub-region II motif since mutation or deletion of sub-region II from the hybrid promoter reduces the level of expression to that observed for the truncated 35S promoter alone. In addition, mutation of the sub-region I sequences in the ARE/35S hybrid promoter does not significantly reduce expression in aerobic conditions, relative to pARE/35S(-90), suggesting that sub-region I does not contribute to this general enhancer function.     

State 1-state 2 adaptation in the cyanobacteria Synechocystis PCC 6714 wild type and Synechocystis PCC 6803 wild type and phycocyanin-less mutant

The mechanism of excitation energy distribution between the two photosystems (state transitions) is studied in Synechocystis 6714 wild type and in wild type and a mutant lacking phycocyanin of Synechocystis 6803. (i) Measurements of fluorescence transients and spectra demonstrate that state transitions in these cyanobacteria are controlled by changes in the efficiency of energy transfer from PS II to PS I (spillover) rather than by changes in association of the phycobilisomes to PS II (mobile antenna model). (ii) Ultrastructural study (freeze-fracture) shows that in the mutant the alignment of the PS II associated EF particles is prevalent in state 1 while the conversion to state 2 results in randomization of the EF particle distribution, as already observed in the wild type (Olive et al. 1986). In the mutant, the distance between the EF particle rows is smaller than in the wild type, probably because of the reduced size of the phycobilisomes. Since a parallel increase of spillover is not observed we suggest that the probability of excitation transfer between PS II units and between PS II and PS I depends on the mutual orientation of the photosystems rather than on their distance. (iii) Measurements of the redox state of the plastoquinone pool in state 1 obtained by PS I illumination and in state 2 obtained by various treatments (darkness, anaerobiosis and starvation) show that the plastoquinone pool is oxidized in state 1 and reduced in state 2 except in starved cells where it is still oxidized. In the latter case, no important decrease of ATP was observed. Thus, we propose that in Synechocystis the primary control of the state transitions is the redox state of a component of the cytochrome b ₆/f complex rather than that of the plastoquinone pool.Abbreviations DCCD dicyclohexylcarbodiimide - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - EF exoplasmic face - PQ plasto-quinone - PS photosystem - PBS phycobilisome     

A Common Region of Deletion on Chromosome 17q in Both Sporadic and Familial Epithelial Ovarian Tumors Distal to BRCA1

Linkage analysis in familial breast and ovarian cancer and studies of allelic deletion in sporadic ovarian tumors have identified a region on chromosome 17q containing a candidate tumor-suppressor gene (referred to as BRCA1) of likely importance in ovarian carcinogenesis. We have examined normal and tumor DNA samples from 32 patients with sporadic and 8 patients with familial forms of the disease, for loss of heterozygosity (LOH) at 21 loci on chromosome 17 (7 on 17p and 14 on 17q). LOH on 17p was 55% (22/40) for informative 17pl3.1 and 17pl3.3 markers. When six polymorphic markers flanking the familial breast/ovarian cancer susceptibility locus on 17ql2-q21 were used, LOH was 58% (23/40), with one tumor showing telomeric retention. Evaluation of a set of markers positioned telomeric to BRCA1 resulted in the highest degree of LOH, 73% (29/40), indicating that a candidate locus involved in ovarian cancer may reside distal to BRCA1. Five of the tumors demonstrating allelic loss for 17q markers were from individuals with a strong family history of breast and ovarian cancer. More important, two of these tumors (unique patient number [UPN] 57 and UPN 79) retained heterozygosity for all informative markers spanning the BRCA1 locus but showed LOH at loci distal to but not including the anonymous markers CMM86 (D17S74) and 42D6 (D17S588), respectively. Deletion mapping of seven cases (two familial and five sporadic) showing limited LOH on 17q revealed a common region of deletion, distal to GH and proximal to D17S4, that spans −25 cM. These results suggest that a potential tumor-suppressor gene involved in both sporadic and familial ovarian cancer may reside on the distal portion of chromosome 17q and is distinct from the BRCA1 gene.     

The Effects of Insertions on Mammalian Intrachromosomal Recombination

We examined the effects of insertion mutations on intrachromosomal recombination. A series of mouse L cell lines carrying mutant herpes simplex virus thymidine kinase (tk) heteroalleles was generated; these lines differed in the nature of their insertion mutations. In direct repeat lines with different large insertions in each gene, there was a 20-fold drop in gene conversion rate and only a five-fold drop in crossover rate relative to the analogous rates in lines with small insertions in each gene. Surprisingly, in direct repeat lines carrying the same large insertion in each gene, there was a larger drop in both types of recombination. When intrachromosomal recombination between inverted repeat tk genes with different large insertions was examined, we found that the rate of gene conversion dropped five-fold relative to small insertions, while the rate of crossing over was unaffected. The differential effects on conversion and crossing over imply that gene conversion is more sensitive to insertion mutation size. Finally, the fraction of gene conversions associated with a crossover increased from 2% for inverted repeats with small insertions to 18% for inverted repeats with large insertions. One interpretation of this finding is that during intrachromosomal recombination in mouse cells long conversion tracts are more often associated with crossing over.     

Interpretation of randomly amplified polymorphic DNA marker data for fingerprinting sweet potato (Ipomoea batatas L.) genotypes

In this paper we present a method for the generation of randomly amplified polymorphic DNA (RAPD) markers for sweet potato. These were applied to produce genetic fingerprints of six clonal cultivars and to estimate genetic distances between these cultivars. The level of polymorphism within the species was extremely high. From the 36-decamer random primers used, 170 fragments were amplified, of which 132 (77.6%) were polymorphic. Ten primers resulted in no detected amplification. Of the remaining 26 primers for which amplification was achieved, only one did not reveal polymorphism. Six primers used alone enabled the discrimination of all six genotypes. Pattern analysis, which employed both a classification and ordination method, enabled the grouping of cultivars and the identification of primers which gave greatest discrimination among the cultivars.     

The F3 Neuronal Glycosylphosphatidylinositol-Linked Molecule Is Localized to Glycolipid-Enriched Membrane Subdomains and Interacts with L1 and Fyn Kinase in Cerebellum

Abstract: The F3 molecule is a member of the immunoglobulin superfamily anchored to plasma membranes by a glycosylphosphatidylinositol group. In adult mouse cerebellum, F3 is predominantly expressed on a subset of axons, the parallel fibers, and at their synapses. In vitro studies established that it is a plurifunctional molecule that, depending on the cellular context and the ligand with which it interacts, either mediates repulsive interactions or promotes neurite outgrowth. In the present study, we report the isolation of two fractions of F3-containing microdomains from adult cerebellum on the basis of their resistance to solubilization by Triton X-100 at 4°C. Both fractions were composed of vesicles, ranging from 100 to 200 nm in diameter. Lipid composition analysis indicated that the lighter fraction was enriched in cerebrosides and sulfatides. F3 sensitivity to phosphatidylinositol phospholipase C differed between the two fractions, possibly reflecting structural differences in the lipid anchor of the F3 molecule. Both fractions were highly enriched in other glycosylphosphatidylinositol-anchored proteins such as NCAM 120 and Thy-1. It is interesting that these vesicles were devoid of the transmembrane forms (NCAM 180 and NCAM 140), which were recovered in Triton X-100-soluble fractions, but contained the L1 transmembrane adhesion molecule that is coexpressed with F3 on parallel fibers and the fyn tyrosine kinase. Immunoprecipitation experiments indicated that F3, but not NCAM 120 or Thy-1, was physically associated in a complex with both L1 and fyn tyrosine kinase. This strongly suggests that the interaction between L1 and F3, already described to occur with isolated molecules, is present in neural tissue. More important is that our study provides information on the molecular machinery likely to be involved in F3 signaling.     

Interruption-deficient mutants of bacteriophage T5 I. Isolation and general properties.

Mutations of bacteriophage T5 were isolated which lack one or more of the natural single-chain interruptions that occur in the mature DNA of this virus. Interruption-deficient mutants were detected by screening survivors of hydroxylamine mutagenesis for altered DNA structure by electrophoresis in agarose slab gels. Over 60 independent mutants were isolated from a survey of approximately 800 phages particles. All of the mutants were viable and could be grouped into two classes. Mutants in one class lacked one of the localized sites where interruptions occur in T5 DNA. To date, mutants that affect five different sites have been obtained. Mutants in the other class were essentially free from interruptions or had a reduced frequency of interruptions throughout the genome. The members of this class included several amber mutants. Complementation tests indicated that at least two genes are required for the presence of interruptions in mature T5 DNA.