Prochlorococcus marinus nov. gen. nov. sp.: an oxyphototrophic marine prokaryote containing divinyl chlorophyll a and b

Several years ago, prochlorophyte picoplankton were discovered in the N. Atlantic. They have since been found to be abundant within the euphotic zone of the world's tropical and temperate oceans. The cells are extremely small, lack phycobiliproteins, and contain divinyl chlorophyll a and b as their primary photosynthetic pigments. Phylogenies constructed from DNA sequence data indicate that these cells are more closely related to a cluster of marine cyanobacteria than to their prochlorophyte relatives Prochlorothrix and Prochloron. Several strains of this organism have recently been brought into culture, and herewith are given the name Prochlorococcus marinus.     

Targeting deletion (homoeologous chromosome pairing locus) or addition line single copy sequences from cereal genomes.

We describe here a protocol for obtaining clones containing sequences present in low copy-number from genomic DNA where moderately and highly repeated sequences predominate. Specific chromosomal regions can be targeted by using deletion or addition line material. We have used this protocol to identify a sequence which has been deleted in both the tetraploid and hexaploid wheat mutants for the homoeologous chromosome pairing locus.     

The 5S DNA units of bread wheat (Triticum aestivum)

A collection of 44 cloned 5S DNA units fromTriticum aestivum cv. Chinese Spring were grouped into 12 sequence-types based on sequence similarity and the respective consensus sequences were then produced. The relationship between these 12 consensus sequences (T. aestivum S 1-S 8 andT. aestivum L 1-L 4), together with two clones sequenced byGerlach andDyer, and the 5S DNA consensus sequences from diploidTriticum spp. were then determined by numerical methods. Both phenetic and cladistic analyses were carried out. The following wheat 5S DNA sequences were found to group with respective sequences from diploidTriticum spp.:T. aestivum S 4, S 6 withT. tauschii S;T. aestivum S 3 withT. monococcum S andT. monococcum S-Rus 7;T. aestivum L 1 andT. aestivum L-G&D withT. speltoides L;T. aestivum L 2, L 3 withT. tauschii L;T. aestivum L 4 withT. monococcum L andT. monococcum L-Rus 12. The analyses suggested that 5 out of the 65S Dna loci present in wheat were identified at the sequence level. The locus that could not be identified in this analysis was the5S Dna-B 1 locus. A group ofT. aestivum sequences (T. aestivum S 1, S 7, S 8, S-G&D) were found to be distinct from the other 5S DNA sequences in the data base. The existence of the distinct group of 5S DNA sequences suggests that there is a gap in our current understanding of wheat evolution with respect to the5S Dna loci.     

Effects of microhabitat and metabolic rate on food intake,growth and fecundity of two competing coral reef fishes

Spinyhead blennies (Acanthemblemaria spinosa) and roughhead blennies (A. aspera) are planktivorous hole-dwelling fishes that live in dead coral skeletons. Both species are known to choose shelters high above the reef surface (although spinyheads displace roughheads downwards). To test the hypothesis that this preference is due to greater plankton availability in higher locations, fish were placed on artificial habitats located 15 cm and 100 cm above the surface of a natural reef. Both species experienced higher feeding rates, growth rates, and fecundities in high locations, and spinyhead rates generally exceeded roughhead rates at a given height. Under laboratory conditions, oxygen consumption by spinyheads was 1.6 times greater than that of roughheads and this corresponds well with the 1.8 ratio of feeding rates under controlled aquarium conditions. This information provides a partial explanation for the observed microhabitat distribution and resulting coexistence of these competing species: it is hypothesized that spinyheads have an advantage in agonistic interactions because of their higher metabolic rates, thus excluding roughheads from high sites, but that roughheads can persist at low sites because their lower metabolic rates result in lower food demands. A model is presented that predicts varying occurrences and vertical distributions of these species in locations with different zooplankton densities.     

The L-isoaspartyl/D-aspartyl protein methyltransferase gene (PCMT1) maps to human chromosome 6q22.3-6q24 and the syntenic region of mouse chromosome 10.

We have mapped the genes for the human and mouse L-isoaspartyl/D-aspartyl protein carboxyl methyltransferase (EC 2.1.1.77) using cDNA probes. We determined that the human gene is present in chromosome 6 by Southern blot analysis of DNA from a panel of mouse-human somatic cell hybrids. In situ hybridization studies allowed us to confirm this identification and further localize the human gene (PCMT1) to the 6q22.3-6q24 region. By analyzing the presence of an EcoRI polymorphism in DNA from backcrosses of C57BL/6J and Mus spretus strains of mice, we localized the mouse gene (Pcmt-1) to chromosome 10, at a position 8.2 +/- 3.5 cM proximal to the Myb locus. This region of the mouse chromosome is homologous to the human 6q24 region.     

Regulation of ANP secretion in insulin-dependent diabetes mellitus and the influence of autonomic neuropathy.

In order to determine the effect of diabetic autonomic neuropathy (DAN) on the atrial natriuretic peptide (ANP) response to dynamic stimuli, we studied the ANP response to 60 degrees head-up and 60 degrees leg-up tilt in diabetic subjects with (DAN + ve, n = 8) and without (DAN - ve, n = 8) evidence of autonomic neuropathy and seven matched non-diabetic controls. Mean baseline plasma ANP concentrations were similar in all three groups. Head-up tilt was associated with a fall in plasma ANP in all seven healthy controls (21.8 (16.8-30.7) to 16.8 (7.1-29.1), P = 0.06, mean (range)), seven of the eight DAN - ve (16.9 (6.5-33.7) to 8.5 (3.0-21.1), P = 0.015) and all eight DAN + ve subjects (27.3 (8.5-101.5) to 15.4 (1.0-67.6), P = 0.044). Leg-up tilt caused a rise in plasma ANP in six of the seven healthy controls (17.6 (7.5-27.9) to 22.4 (15.2-48.1), P = 0.041), six of the eight DAN - ve (12.5 (7.8-27.8) to 15.5 (7.3-31.3), P = 0.054) and seven of the eight DAN + ve subjects (18.2 (2.8-55.1) to 25.1 (4.5-92.8), P = 0.013). There was no significant difference in the fall in plasma ANP during head-up tilt or in the rise in plasma ANP during leg-up tilt between the three groups. We conclude that the regulation of ANP secretion is normal in diabetes mellitus, and is unaffected by the presence of autonomic neuropathy.     

Charge balance in the alpha-hydroxyacid dehydrogenase vacuole: an acid test.

The proposal that the active site vacuole of NAD(+)-S-lactate dehydrogenase is unable to accommodate any imbalance in electrostatic charge was tested by genetically manipulating the cDNA coding for human muscle lactate dehydrogenase to make a protein with an aspartic acid introduced at position 140 instead of the wild-type asparagine. The Asn 140-Asp mutant enzyme has the same kcat as the wild type (Asn 140) at low pH (4.5), and at higher pH the Km for pyruvate increases 10-fold for each unit increase in pH up to pH 9. We conclude that the anion of Asp 140 is completely inactive and that it binds pyruvate with a Km that is over 1,000 times that of the Km of the neutral, protonated aspartic-140. Experimental results and molecular modeling studies indicate the pKa of the active site histidine-195 in the enzyme-NADH complex is raised to greater than 10 by the presence of the anion at position 140. Energy minimization and molecular dynamics studies over 36 ps suggest that the anion at position 140 promotes the opening of and the entry of mobile solvent beneath the polypeptide loop (98-110), which normally seals off the internal active site vacuole from external bulk solvent.     

Induction of gene expression in Dictyostelium by prestarvation factor, a factor secreted by growing cells

During growth, Dictyostelium cells continuously secrete a factor, PSF, that accumulates in proportion to cell density. At sufficient concentration, it triggers the production of discoidin I and certain lysosomal enzymes. Our earlier studies demonstrated these effects of PSF on protein and enzyme levels [Clarke et al., Differentiation 34:79-87, 1987; Clarke et al., Dev Genet 9: 315-326, 1988]. In the present study, we have examined whether PSF induces increased mRNA levels. By Northern blot analysis, we have found that discoidin I mRNA accumulates in exponentially growing NC4 cells as the cells reach high density; significant levels of mRNA are detectable in cells growing either on plates or in suspension, beginning about four generations before the end of exponential growth. High levels of discoidin I mRNA are also found in low-density cells grown in the presence of buffer conditioned by high-density cells. These results indicate that PSF induces the accumulation of discoidin I mRNA. Other "early developmental" genes, pCZ22 and the early I genes (16, 18, and 111), are also expressed in exponentially growing cells at high density or in the presence of conditioned buffer. We conclude that several genes previously found to be preferentially expressed very early in development are actually induced during late exponential growth by PSF.