A 43 kDa DNA binding protein from the pea chloroplast interacts with and stimulates the cognate DNA polymerase.

A DNA binding protein with DNA polymerase 'accessory activity' has been identified and purified to apparent homogeneity from pea chloroplasts. This protein consists of a single subunit of 43 kDa and binds to DNA regardless of its base sequence and topology. It increases cognate DNA polymerase-primase activity in a dose dependent manner. Using solid phase protein-protein interaction trapping and co-immunoprecipitation techniques, the purified protein was found to associate with the chloroplast DNA polymerase. The chloroplast DNA polymerase also binds directly to the radioiodinated 43 kDa protein. The specific interaction between 43 kDa protein and chloroplast DNA polymerase results in the synthesis of longer DNA chains. The 43 kDa protein, present abundantly in the pea chloroplast, appears to increase processivity of the chloroplast DNA polymerase and may play an important role in the replication of pea chloroplast DNA.     

Repression by a differentiation-specific factor of the human cytomegalovirus enhancer.

We detected a novel nuclear protein, MRF, that binds to multiple sites on the modulator which is located upstream of the human cytomegalovirus major immediate early gene enhancer. The expression of MRF is differentiation specific; the DNA binding activity is present in nuclear extracts from undifferentiated Tera-2 and THP-1 cells, but significantly reduced after these cells are induced to differentiate. In undifferentiated cells the enhancer activity is repressed by the modulator and upon differentiation the enhancer becomes active. Competitive binding assays demonstrate that MRF requires the presence of multiple A+T stretches for binding to DNA, rather than binding to a specific DNA sequence. Mutations of these stretches in the modulator reduce the binding activity of MRF, as well as the repressing activity on the enhancer. These results suggest that MRF may act as a repressor of enhancer function. We propose that MRF binds over the entire modulator and exerts repressor activity.     

On the existence of stable pairing distributions

We formulate and analyze pair-formation models for multiple groups with general pairing rates and arbitrary mixing probabilities. Under the assumption of constant recruitment rates and equal average duration of all types of partnerships, we have shown that the dynamics are relatively simple because of the monotonicity properties of the dynamical system associated with the pairing/mixing of heterogeneous populations of male and female individuals. In fact, we have shown that the corresponding asymptotic stable paired distribution is given precisely by the asymptotic values of the matrices that prescribe the mixing/contact structure. In other words, if the sizes of the mixing subpopulations of males and females are asymptotically constant and if the average durations of partnerships are about the same regardless of type, then the matrices that describe the mixing between subpopulations also characterize the distribution of paired types. Alternatively, if the distribution of the average duration of relationships between individuals has a large variance then it may be impossible to detect any relationship between the mixing/contact structure and the observed distribution of paired types. The study of models with constant per-capita recruitment rates give rise to homogeneous systems of degree one. The analysis of the dynamics of pairs for models with exponentially growing populations of singles is complicated. So far, we are only able to classify the stability of all non-strictly positive boundary exponential solutions. From our incomplete analysis, it is not possible to detect necessary and sufficient conditions for the existence and stability of strictly interior exponential solutions. We cannot rule out the possibility of oscillations. The mathematical problems associated with the stability of exponential solutions of dynamical systems of degree one are of relevance in demography, epidemiology, and population dynamics.On leave from University of Alabama in Huntsville     

生物复苏——大绝灭后生物演化历史的第一幕

生命史是一部生物界短期,快速剧变与长期,慢速稳定相互交替的历史。大绝灭（即集群绝灭）事件反映了全球环境的大突变,点断了地质历史中的生命记录及其发展历程,预示着生物界的演化出现了最有意义的飞跃,近年来尝试研究大绝灭后全球生物界的残存－复苏及其基本型式,并探索复苏的控制因素,标志着地质科学中一个重心的转移（即从大绝灭转向其后的生物残存与复苏的研究）。生物复苏揭示了大绝灭后生物演化历史的第一幕,其研究的     

Molecular definition of red cell Rh haplotypes by tightly linked SphI RFLPs.

The Rh blood group system of human red cells contains five major antigens D, C/c, and E/e (the latter four designated "non-D") that are specified by eight gene complexes known as Rh haplotypes. In this paper, we report on the mapping of RH locus and identification of a set of SphI RFLPs that are tightly linked with the Rh structural genes. Using exon-specific probes, we have localized the SphI cleavage sites resulting in these DNA markers and derived a comprehensive map for the RH locus. It was found that the SphI fragments encompassing exons 4-7 of the Rh genes occur in four banding patterns or frameworks that correspond to the distribution and segregation of the common Rh haplotypes. This linkage disequilibrium allowed a genotype-phenotype correlation and direct determination of Rh zygosity related to the Rh-positive or Rh-negative status (D/D, D/d, and d/d). Studies on the occurrence of SphI RFLPs in a number of rare Rh variants indicated that Rh phenotypic diversity has taken place on different haplotype backgrounds and has arisen by diverse genetic mechanisms. The molecular definition of Rh haplotypes by SphI RFLP frameworks should provide a useful procedure for genetic counseling and prenatal assessment of Rh alloimmunization.     

Growth-Associated Production of Poly(3-Hydroxyvalerate) from n-Pentanol by a Methylotrophic Bacterium, Paracoccus denitrificans

Paracoccus denitrificans accumulated a polyester in its cells during growth on n-pentanol. The composition of the polyester varied during the cultivation: the level of the 3-hydroxyvalerate unit in the polyester increased, and eventually a homopolymeric poly(3-hydroxyvalerate) [P(3HV)] accumulated to an amount 22 to 24% of the cell dry weight. Growth-associated polyester synthesis was considerably affected by n-pentanol when its concentration was controlled at several levels. Maximum accumulation of the polyester was obtained at 0.02% (vol/vol). Physical and mechanical characteristics of the P(3HV) were determined and compared with those of other homo- and copolyesters. The P(3HV) was dextrorotatory and had number-averaged and weight-averaged molecular masses of 128,000 and 888,000 Da, respectively, with a rate of polydispersity of 6.93. The level of tensile strength of the P(3HV) was lower, and its extension to break was higher than that of the poly(3-hydroxybutyrate) homopolyester.     

Myosin VIIA mutation screening in 189 Usher syndrome type 1 patients.

Usher syndrome type 1b (USH1B) is an autosomal recessive disorder characterized by congenital profound hearing loss, vestibular abnormalities, and retinitis pigmentosa. The disorder has recently been shown to be caused by mutations in the myosin VIIa gene (MYO7A) located on 11q14. In the current study, a panel of 189 genetically independent Usher I cases were screened for the presence of mutations in the N-terminal coding portion of the motor domain of MYO7A by heteroduplex analysis of 14 exons. Twenty-three mutations were found segregating with the disease in 20 families. Of the 23 mutations, 13 were unique, and 2 of the 13 unique mutations (Arg212His and Arg212Cys) accounted for the greatest percentage of observed mutant alleles (8/23, 31%). Six of the 13 mutations caused premature stop codons, 6 caused changes in the amino acid sequence of the myosin VIIa protein, and 1 resulted in a splicing defect. Three patients were homozygotes or compound heterozygotes for mutant alleles; these three cases were Tyr333Stop/Tyr333Stop, Arg212His-Arg302His/Arg212His-Arg302His, and IVS13nt-8c-->g/Glu450Gln. All the other USH1B mutations observed were simple heterozygotes, and it is presumed that the mutation on the other allele is present in the unscreened regions of the gene. None of the mutations reported here were observed in 96 unrelated control samples, although several polymorphisms were detected. These results add three patients to single case reported previously where mutations have been found in both alleles and raises the total number of unique mutations in MYO7A to 16.     

Simultaneous Determination of Dermatan Sulfate and Oversulfated Dermatan Sulfate in Plasma by High-Performance Liquid Chromatography with Postcolumn Fluorescence Derivatization

A chemical method for the determination of dermatan sulfate (DS) and oversulfated dermatan sulfate has been developed and applied to the pharmacokinetic study of these polysaccharides in experimental animals. The analytical procedure includes a simple preparation step of administered DS and oversulfated DS from blood plasma, HPLC for the separation and detection of DS and oversulfated DS using an Asahipak NH₂P-50 column, fluorometric reaction of the polysaccharides with guanidine in a strong alkaline medium. DS and oversulfated DS were extracted from plasma by treating it with proteinase to remove plasma proteins and recovered with endogenous plasma glycosaminoglycans by ethanol precipitation. Finally, DS and oversulfated DS were analyzed by fluorometric HPLC. The detection limits of DS and oversulfated DS were 10 and 20 ng, respectively. Furthermore, we demonstrated that artificial oversulfation of DS increased its biological half-life after intravenous administration to rats.     

Detection of membrane packing defects by time-resolved fluorescence depolarization.

Packing defects in lipid bilayer play a significant role in the biological activities of cell membranes. Time-resolved fluorescence depolarization has been used to detect and characterize the onset of packing defects in binary mixtures of dilinoleoylphosphatidylethanolamine/1-palmitoyl-2- oleoylphosphatidylcholine (PE/PC). These PE/PC mixtures exhibit mesoscopic packing defect state (D), as well as one-dimensional lambellar liquid crystalline (L alpha) and two-dimensional inverted hexagonal (HII) ordered phases. Based on previous electron microscopic investigations, this D state is characterized by the presence of interlamellar attachments and precursors of HII phase between the lipid layers. Using a rotational diffusion model for rod-shaped fluorophore in a curved matrix, rotational dynamics parameters, second rank order parameter, localized wobbling diffusion, and curvature-dependent rotational diffusion constants of dipyenylhexatriene (DPH)-labeled PC (DPH-PC) in the host PE/PC matrix were recovered from the measured fluorescence depolarization decays of DPH fluorescence. At approximately 60% PE, abrupt increases in these rotational dynamics parameters were observed, reflecting the onset of packing defects in the host PE/PC matrix. We have demonstrated that rotational dynamics parameters are very sensitive in detecting the onset of curvature-associating packing defects in lipid membranes. In addition, the presence of the D state can be characterized by the enhanced wobbling diffusional motion and order packing of lipid molecules, and by the presence of localized curvatures in the lipid layers.