In vitro and in vivo evidence for lack of endovascular remodeling by third trimester trophoblasts

The placental-decidual interaction through invading trophoblasts determines whether a physiological transformation of the uterine spiral arteries is established or not. Trophoblast-orchestrated artery remodeling is central to normal placentation. Dysregulated uteroplacental interaction and vascular remodeling are thought to be associated with the molecular events underlying the pathology of late pregnancy anomalies including preeclampsia. Although the exact gestational age at which trophoblast invasion ceases is not known, it remains unclear whether late pregnancy trophoblasts retain the ability to transform the uterine arteries. Here, we have developed a dual cell, in vitro culture system that mimics the vascular remodeling events during normal pregnancy. We demonstrate that first and third trimester trophoblasts respond differentially to interactive signals from endothelial cells when cultured on matrigel. Term primary trophoblasts or immortalized third trimester extravillous TCL1 trophoblasts not only fail to respond to signals from endothelial cells but also inhibit endothelial cell tube formation. In contrast, HTR8 cells, representing a first trimester trophoblast cell line with invasive properties, undergo spontaneous migration and synchronize with the endothelial cells in a capillary network. This disparity in behavior was confirmed in vivo using a matrigel plug assay. Poor expression of VEGF C and VEGF receptors coupled with high E-cadherin expression by term primary trophoblasts and TCL1 cells contributed to their restricted interactive and migratory properties. We further show that the kinase activity of VEGF R2 is essential for proactive crosstalk by HTR8 cells. This unique behavior of first trimester trophoblasts in the presence of endothelial cells offers a potential approach to study cell-cell interactions and to decipher modulatory components in the serum samples from adverse pregnancy outcomes.

FAP mutations destabilize transthyretin facilitating conformational changes required for amyloid formation

Functional transthyretin (TTR) can be transformed into amyloid by partial acid denaturation yielding a monomeric amyloidogenic intermediate which self-associates. The amyloidogenic intermediate has substantial beta-sheet structure with non-native but defined tertiary structure. pH-dependent proteolysis sensitivity studies have identified portions of TTR which become disordered and solvent-exposed in the amyloidogenic intermediate. These include the C-strand-loop D-strand portion of TTR which moves away from the core of the beta-sandwich fold. Mutations that are associated with early onset-amyloid disease (familial amyloidotic polyneuropathy; FAP) function by destabilizing tetrameric TTR in favour of the monomeric amyloidogenic intermediate which has a rearranged C-strand-loop D-strand region. In most cases the FAP mutations do not significantly alter the native folded structure, but instead act on the denaturation pathway by a mechanism that is not completely understood. Interestingly, mutations have also been characterized which strongly stabilize tetrameric TTR and make amyloid formation very difficult at pHs accessible in vivo.

Identification and chromosomal location of major genes for resistance to Pyrenophora teres in a doubled-haploid barley population

Net blotch, caused by Pyrenophora teres, is one of the most economically important diseases of barley worldwide. Here, we used a barley doubled-haploid population derived from the lines SM89010 and Q21861 to identify major quantitative trait loci (QTLs) associated with seedling resistance to P. teres f. teres (net-type net blotch (NTNB)) and P. teres f. maculata (spot-type net blotch (STNB)). A map consisting of simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) markers was used to identify chromosome locations of resistance loci. Major QTLs for NTNB and STNB resistance were located on chromosomes 6H and 4H, respectively. The 6H locus (NTNB) accounted for as much as 89% of the disease variation, whereas the 4H locus (STNB resistance) accounted for 64%. The markers closely linked to the resistance gene loci will be useful for marker-assisted selection.

Identification and mapping of SNPs from ESTs in sunflower

More than 67,000 expressed sequence tags (ESTs) have recently been generated for sunflower (Helianthus), including 44,000 from cultivated confectionery (RHA280) and oilseed (RHA801) lines of Helianthus annuus and 23,000 from drought- and salt-tolerant wild sunflowers, H. argophyllus and H. paradoxus, respectively. To create a transcript map for sunflower, we identified 605 ESTs that displayed small insertion-deletion polymorphism (SNP) variation in silico, had apparent tissue-specific expression patterns, and/or were ESTs with candidate functions in traits such as development, cell transport, metabolism, plant defense, and tolerance to abiotic stress. Primer pairs for 535 of the loci were designed from the ESTs and screened for polymorphism in recombinant inbred lines derived from a cross between the same cultivars (RHA280 x RHA801) employed for sequencing. In total, 273 of the loci amplified polymorphic products, of which 243 mapped to the 17 linkage groups previously identified for sunflower. Comparisons with previously mapped QTL revealed some cases where ESTs with putatively related functions mapped near QTLs identified in other crosses for salt tolerance and for domestication traits such as stem diameter, shattering, flowering time, and achene size.

Erratum to: Traffic injury data, policy, and public health: Lessons from Boston Chinatown

In the March 2002 issue, the following credit line was omitted from Fig. 1(a) on p. 90 (Brugge D, Lai Z, Hill, C, Rand W. Traffic Injury Data, Policy, and Public Health: Lessons from Boston Chinatown. J Urban Health. 2002;79(1):87-103): "This figure is reprinted with permission from Brugge D, A Leong, Z Lai. Can a community inject public health values into transportation questions? Public Health Rep. 1999:114:44."

Design of a compartmentalized shotgun assembler for the human genome

Two different strategies for determining the human genome are currently being pursued: one is the "clone-by-clone" approach, employed by the publicly funded project, and the other is the "whole genome shotgun assembler" approach, favored by researchers at Celera Genomics. An interim strategy employed at Celera, called compartmentalized shotgun assembly, makes use of preliminary data produced by both approaches. In this paper we describe the design, implementation and operation of the "compartmentalized shotgun assembler".

Human mdm2 mediates multiple mono-ubiquitination of p53 by a mechanism requiring enzyme isomerization

The mdm2 gene product is an important regulator of p53 function and stability. mdm2 is an E3 ubiquitin ligase for p53 and the RING finger domain of mdm2 is critical for ligase activity. Ubiquitin (Ub) conjugation is a general targeting modification and poly-ubiquitin chains specifically target proteins to the proteasome for degradation. In this report, we show that the multistep cascade of mdm2-mediated p53 ubiquitination can be reduced to three purified recombinant proteins: ubiquitin-conjugated E2, mdm2, and p53. This simplification allows enzymatic analysis of the isolated ligase reaction. The simplified reaction recapitulates the ubiquitination of p53 observed with individual components and the p53-Ub((n)) is qualitatively similar to p53-Ub((n)) detected in lactacystin-treated cells. Surprisingly, we find that p53 is modified with multiple mono-ubiquitin moieties as opposed to a poly-ubiquitin chain. Finally, kinetic analysis indicates the transfer reaction proceeds either through a modified Ping Pong mechanism involving requisite enzyme isomerization steps, or through a Rapid Equilibrium Random Bi Bi mechanism involving very large anti-cooperative interactions between the two substrate binding pockets on the enzyme, mediated through allosteric changes in enzyme structure.

[Helicobacter pylori associated gastric mucosal inflammation and histopathological assessment]

OBJECTIVE

To investigate the pathological features of Helicobacter pylori associated gastric mucosal inflammation and to establish relevant histopathological assessment standards.

METHODS

Biopsy specimens from the gastric antrum, body of stomach, and gastric angle were taken from 2 134 cases of H. pylori associated gastric mucosal inflammation. H. pylori was identified by means of rapid urase test and toluidine blue staining or immunohistological staining. The severity of mucosal inflammation was evaluated with HE staining. Ultrastucture evaluation was conducted for part of the specimens.

RESULTS

In H. pylori positive cases lymphocytic infiltration could be observed in glandulous epithelium. which was not found in normal gastric mucosa. Scoring of severity of mucosal inflammation reflected the status of H. pylori infection and was not influenced by the biopsy site, size of specimen, and direction of sectioning. Severe active inflammation could be seen in 39.6% of the H. pylori positive cases, and 0.4% of the H. pylori negative cases. The severity score of inflammation was significantly correlated with the amount of H. pylori colonization.

CONCLUSION

Reflecting the real status of H. pylori associated mucosal inflammation. The grading method reported here is simple, reliable, and easy to master.

[Effects of vascular endothelial growth factor on adhesion molecular expression of hepatocellular carcinoma HepG]

OBJECTIVE

To study the effect of vascular endothelial growth factor (VEGF) on homotypic adhesion and E-cadherin of hepatocellular carcinoma cells.

METHODS

We measured the function of homotypic adhesion with (3)H-TdR infiltration and the expression of E-cadherin with laser scanning confocal microscope.

RESULTS

After 60, 90, 120min, the values (dpm/min) of (3)H-TdR infiltration in HepG(2) cells induced by 1ng/ml, 5ng/ml VEGF were 1758.67+/-289.46, 1380.03+/-328.55, 2657.43 +/- 310.31 and 3124.30+/-262.14, 2245.60+/-273.24, 2091.52+/-213.84. The values by 10ng/ml VEGF were 1232.32+/-201.04, 2337.50+/-333.04, 2236.99 +/- 237.07, which were significantly lower than those in control group (P<0.05 or 0.01). The expression of E-cadherin in hepatocellular carcinoma cells induced by 5ng/ml VEGF was 352+/-56 and much lower than that in control group (757+/-103, P<0.01).

CONCLUSIONS

VEGF can decrease homotopic adhesion of hepatocellular carcinoma HepG(2) cell, which is connected with the less expression of E-cadherin in hepatocellular carcinoma HepG(2) cell.

[The mutation of anti-CD3 antibody (HIT3a) gene and its expression]

OBJECTIVE

To improve the expression of anti-CD(3) single chain Fv (scFv) by site mutation and identify its biological activity.

METHODS

Anti-CD(3) scFv gene was mutated by PCR, the target clones were screened by both the fingerprints of DNA restriction endonuclease digestion and Western blot, the antigen-binding activity of scFv was examined by FACS, competitive inhibition was performed with (125)I-labeled HIT3a and the cytotoxic effect mediated by the anti-CD(3) scFv-activated T lymphocytes was analyzed by (51)Cr-released assays.

RESULTS

The DNA sequencing showed that the 6th amino acid of the anti-CD(3) antibody (HIT3a) heavy chain gene was mutated from E (GAG) to Q (CAG). The expression of mutated anti-CD(3) scFv (m2) was increased by 100 times higher than that of the parent scFv, and there was no difference in the Jurkat cell (CD(3)(+))-binding activity between the (m2) and parent scFv. The preliminary results of competitive assays showed that m2 could partially block the sites of CD(3)(+) Jurkat cells where the parent antibody bound to. Cytotoxicity assays demonstrated that CD(3)AK cells induced by IL-2 and m2 showed stronger cytotoxic effect than that of LAK cells induced by IL-2 alone in vitro.

CONCLUSION

By site mutation, a high expression fragment m2 of anti-CD(3) scFv antibody was obtained. The results of some experiments indicated that m2 could bind to CD(3)(+) Jurkat cells, furthermore, by co-stimulated with IL-2, it could activate peripheral T lymphocytes and induce CD(3)AK cytotoxic effect.

The sequence of the human genome

A 2.91-billion base pair (bp) consensus sequence of the euchromatic portion of the human genome was generated by the whole-genome shotgun sequencing method. The 14.8-billion bp DNA sequence was generated over 9 months from 27,271,853 high-quality sequence reads (5.11-fold coverage of the genome) from both ends of plasmid clones made from the DNA of five individuals. Two assembly strategies-a whole-genome assembly and a regional chromosome assembly-were used, each combining sequence data from Celera and the publicly funded genome effort. The public data were shredded into 550-bp segments to create a 2.9-fold coverage of those genome regions that had been sequenced, without including biases inherent in the cloning and assembly procedure used by the publicly funded group. This brought the effective coverage in the assemblies to eightfold, reducing the number and size of gaps in the final assembly over what would be obtained with 5.11-fold coverage. The two assembly strategies yielded very similar results that largely agree with independent mapping data. The assemblies effectively cover the euchromatic regions of the human chromosomes. More than 90% of the genome is in scaffold assemblies of 100,000 bp or more, and 25% of the genome is in scaffolds of 10 million bp or larger. Analysis of the genome sequence revealed 26,588 protein-encoding transcripts for which there was strong corroborating evidence and an additional approximately 12,000 computationally derived genes with mouse matches or other weak supporting evidence. Although gene-dense clusters are obvious, almost half the genes are dispersed in low G+C sequence separated by large tracts of apparently noncoding sequence. Only 1.1% of the genome is spanned by exons, whereas 24% is in introns, with 75% of the genome being intergenic DNA. Duplications of segmental blocks, ranging in size up to chromosomal lengths, are abundant throughout the genome and reveal a complex evolutionary history. Comparative genomic analysis indicates vertebrate expansions of genes associated with neuronal function, with tissue-specific developmental regulation, and with the hemostasis and immune systems. DNA sequence comparisons between the consensus sequence and publicly funded genome data provided locations of 2.1 million single-nucleotide polymorphisms (SNPs). A random pair of human haploid genomes differed at a rate of 1 bp per 1250 on average, but there was marked heterogeneity in the level of polymorphism across the genome. Less than 1% of all SNPs resulted in variation in proteins, but the task of determining which SNPs have functional consequences remains an open challenge.

[The evaluation of cagA and other vaccine candidate proteins of Helicobacter pylori on T cell apoptosis mediated by Fas/Fas ligand interaction]

OBJECTIVE

To evaluate the effect of several surface proteins of Helicobacter pylori (H. pylori) on inducing apoptosis of T cells through the modulation of Fas/Fas ligand (FasL) interaction and to provide information on the screen of safe and effective immunogen for H. pylori vaccine.

METHODS

T cell apoptosis induced by cagA+ and isogenic cagA knockout strain, recombinant urease, HpaA and outer membrane proteins, Hop25, Hop35 and Hop38 was detected by JAM assay. Flow cytometry was used to evaluate the increase in FasL expression on T cells under the stimulation of these bacterial proteins. Metalloprotease inhibitor, 1, 10-Phenanthroline (PHE) and protein synthesis inhibitor, emetine, were used to change the activity of FasL to confirm the association of FasL with H. pylori mediated killing toward T cells.

RESULTS

The effect of cagA+ H. pylori was stronger in both the induction of apoptosis and FasL expression of T cells than that of cagA knockout strain. H. pylori urease could not kill T cell, while Hop38 had the strongest effect among the tested H. pylori proteins on the induction of T cell apoptosis through increasing FasL expression. Metaloprotease inhibitor could increase the killing of T cells induced by H. pylori because of its ability to prevent the cleavage of membrane-bound FasL protein. On the other hand, emetine could decrease H. pylori mediated killing by inhibiting of FasL synthesis on T cells.

CONCLUSION

cagA and Hop38 protein might be involved in the negative regulation of T cell growth through upregulating FasL expression urease and other Hop proteins tested might be safe and effective to be used as the antigens for H. pylori vaccine.

Development of multigene and regulated lentivirus vectors

Previously we described safe and efficient three-component human immunodeficiency virus type 1 (HIV-1)-based gene transfer systems for delivery of genes into nondividing cells (H. Mochizuki, J. P. Schwartz, K. Tanaka, R. O. Brady, and J. Reiser, J. Virol. 72:8873-8883, 1998). To apply such vectors in anti-HIV gene therapy strategies and to express multiple proteins in single target cells, we have engineered HIV-1 vectors for the concurrent expression of multiple transgenes. Single-gene vectors, bicistronic vectors, and multigene vectors expressing up to three exogenous genes under the control of two or three different transcriptional units, placed within the viral gag-pol coding region and/or the viral nef and env genes, were designed. The genes encoding the enhanced version of green fluorescent protein (EGFP), mouse heat-stable antigen (HSA), and bacterial neomycin phosphotransferase were used as models whose expression was detected by fluorescence-activated cell sorting, fluorescence microscopy, and G418 selection. Coexpression of these reporter genes in contact-inhibited primary human skin fibroblasts (HSFs) persisted for at least 6 weeks in culture. Coexpression of the HSA and EGFP reporter genes was also achieved following cotransduction of target cells using two separate lentivirus vectors encoding HSA and EGFP, respectively. For the regulated expression of transgenes, tetracycline (Tet)-regulatable lentivirus vectors encoding the reverse Tet transactivator (rtTA) and EGFP controlled by a Tet-responsive element (TRE) were constructed. A binary HIV-1-based vector system consisting of a lentivirus encoding rtTA and a second lentivirus harboring a TRE driving the EGFP reporter gene was also designed. Doxycycline-modulated expression of the EGFP transgene was confirmed in transduced primary HSFs. These versatile vectors can potentially be used in a wide range of gene therapy applications.

I. The neurocognitive profile of Williams Syndrome: a complex pattern of strengths and weaknesses

The rare, genetically based disorder, Williams syndrome (WMS), produces a constellation of distinctive cognitive, neuroanatomical, and electrophysiological features which we explore through the series of studies reported here. In this paper, we focus primarily on the cognitive characteristics of WMS and begin to forge links among these characteristics, the brain, and the genetic basis of the disorder. The distinctive cognitive profile of individuals with WMS includes relative strengths in language and facial processing and profound impairment in spatial cognition. The cognitive profile of abilities, including what is 'typical' for individuals with WMS is discussed, but we also highlight areas of variability across the group of individuals with WMS that we have studied. Although the overall cognitive abilities (IQs) of individuals with WMS are typically in the mild-to-moderate range of mental retardation, the peaks and valleys within different cognitive domains make this syndrome especially intriguing to study across levels. Understanding the brain basis (and ultimately the genetic basis) for higher cognitive functioning is the goal we have begun to undertake with this line of interdisciplinary research.

VI. Genome structure and cognitive map of Williams syndrome

Williams syndrome (WMS) is a most compelling model of human cognition, of human genome organization, and of evolution. Due to a deletion in chromosome band 7q11.23, subjects have cardiovascular, connective tissue, and neurodevelopmental deficits. Given the striking peaks and valleys in neurocognition including deficits in visual-spatial and global processing, preserved language and face processing, hypersociability, and heightened affect, the goal of this work has been to identify the genes that are responsible, the cause of the deletion, and its origin in primate evolution. To do this, we have generated an integrated physical, genetic, and transcriptional map of the WMS and flanking regions using multicolor metaphase and interphase fluorescence in situ hybridization (FISH) of bacterial artificial chromosomes (BACs) and P1 artificial chromosomes (PACs), BAC end sequencing, PCR gene marker and microsatellite, large-scale sequencing, cDNA library, and database analyses. The results indicate the genomic organization of the WMS region as two nested duplicated regions flanking a largely single-copy region. There are at least two common deletion breakpoints, one in the centromeric and at least two in the telomeric repeated regions. Clones anchoring the unique to the repeated regions are defined along with three new pseudogene families. Primate studies indicate an evolutionary hot spot for chromosomal inversion in the WMS region. A cognitive phenotypic map of WMS is presented, which combines previous data with five further WMS subjects and three atypical WMS subjects with deletions; two larger (deleted for D7S489L) and one smaller, deleted for genes telomeric to FZD9, through LIMK1, but not WSCR1 or telomeric. The results establish regions and consequent gene candidates for WMS features including mental retardation, hypersociability, and facial features. The approach provides the basis for defining pathways linking genetic underpinnings with the neuroanatomical, functional, and behavioral consequences that result in human cognition.

IV. Neuroanatomy of Williams syndrome: a high-resolution MRI study

Williams syndrome (WMS), a genetic condition resulting from a contiguous deletion on the long arm of chromosome 7, is associated with a relatively consistent profile of neurocognitive and neurobehavioral features. The distinctiveness and regularity of the profile of learning and behavioral characteristics in this genetic condition suggests that underlying neurobiological correlates may be identifiable. In this initial study, we report findings derived from a high-resolution neuroimaging study of 14 young adult subjects with WMS and an individually matched normal control group. Compared to controls, subjects with WMS were noted to have decreased overall brain and cerebral volumes, relative preservation of cerebellar and superior temporal gyrus (STG) volumes, and disproportionate volume reduction of the brainstem. Analyses also suggested that the pattern of cerebral lobe proportions in WMS may be altered compared to normal controls with a greater ratio of frontal to posterior (parietal+occipital) tissue. Assessment of tissue composition indicated that, relative to controls, individuals with WMS have relative preservation of cerebral gray matter volume and disproportionate reduction in cerebral white matter volume. However, within the cerebral gray matter tissue compartment, the right occipital lobe was noted to have excess volume loss. Combined with our growing knowledge of the function of genes in the commonly deleted region for WMS, more detailed information regarding the structure and function of the WMS brain will provide a unique opportunity for elucidating meaningful correlations amongst genetic, neurobiological, and neurobehavioral factors in humans.

II. Hypersociability in Williams Syndrome

Studies of abnormal populations provide a rare opportunity for examining relationships between cognition, genotype and brain neurobiology, permitting comparisons across these different levels of analysis. In our studies, we investigate individuals with a rare, genetically based disorder called Williams syndrome (WMS) to draw links among these levels. A critical component of such a cross-domain undertaking is the clear delineation of the phenotype of the disorder in question. Of special interest in this paper is a relatively unexplored unusual social phenotype in WMS that includes an overfriendly and engaging personality. Four studies measuring distinct aspects of hypersocial behavior in WMS are presented, each probing specific aspects in WMS infants, toddlers, school age children, and adults. The abnormal profile of excessively social behavior represents an important component of the phenotype that may distinguish WMS from other developmental disorders. Furthermore, the studies show that the profile is observed across a wide range of ages, and emerges consistently across multiple experimental paradigms. These studies of hypersocial behavior in WMS promise to provide the groundwork for crossdisciplinary analyses of gene-brain-behavior relationships.

Intercellular delivery of a herpes simplex virus VP22 fusion protein from cells infected with lentiviral vectors

Effective gene therapy depends on the efficient transfer of therapeutic genes and their protein products to target cells. Lentiviral vectors appear promising for virus-mediated gene delivery and long-term expression in nondividing cells. The herpes simplex virus type 1 tegument protein VP22 has recently been shown to mediate intercellular transport of proteins, raising the possibility that it may be helpful in a setting where the global delivery of therapeutic proteins is desired. To investigate the effectiveness of lentiviral vectors to deliver genes encoding proteins fused to VP22, and to test whether the system is sufficiently potent to allow protein delivery from transduced cells in vitro and in vivo, fusion constructs of VP22 and the enhanced green fluorescent protein (EGFP) were prepared and delivered into target cells by using HIV-1-based lentiviral vectors. To follow the spread of VP22-EGFP to other cells, transduced COS-7 cells were coplated with a number of different cell types, including brain choroid plexus cells, human endothelial cells, H9 cells, and HeLa cells. We found that VP22-EGFP fusion proteins were transported from transduced cells to recipient cells and that such fusion proteins accumulated in the nucleus and in the cytoplasm of such cells. To determine the ability to deliver fusion proteins in vivo, we injected transduced H9 cells as well as the viral vector directly into the brain of mice. We present evidence that VP22-EGFP fusion proteins were transported effectively from lentivirus transduced cells in vivo. We also show that the VP22-EGFP fusion protein encoded by the lentivirus is transported between cells. Our data indicate that such fusion proteins are present in the nucleus and in the cytoplasm of neighboring cells. Therefore, lentiviral vectors may provide a potent biological system for delivering genes encoding therapeutic proteins fused to VP22.

The Drosophila homolog of Onecut homeodomain proteins is a neural-specific transcriptional activator with a potential role in regulating neural differentiation

We report here the characterization of the Drosophila homolog of the onecut homeobox gene, which encodes a protein product with one cut domain and one homeodomain. We present evidence that D-Onecut can bind to similar DNA sequences with high specificity and affinity as other Onecut proteins through the highly conserved cut domain and homeodomain. Interestingly, the cut domain alone can mediate DNA-binding, but the homeodomain cannot. However, depending upon the promoter context, we observed cooperative interactions between the two domains to confer high DNA-binding affinity and specificity. D-Onecut appears to be a moderate transcriptional activator and functions as a nuclear protein in neuronal tissues of both the CNS and PNS during development and in the adult. In the eye, D-Onecut expression is independent of glass, a transcriptional regulator of R cell differentiation. Taken together, our results suggest a role for D-Onecut in the regulation of some aspects of neural differentiation or maintenance. In support of this notion, overexpression of a putative dominant negative form of D-Onecut during eye development does not affect early cell fate specification, but severely affects photoreceptor differentiation.

Thermodynamics of p53 binding to hdm2(1-126): effects of phosphorylation and p53 peptide length

Upon exposure to DNA-damaging agents, the p53 tumor suppressor protein is stabilized and activated, leading to cell cycle arrest, DNA repair, or apoptosis. One of the major factors that regulates the level and the transcriptional activity of p53 is the hdm2 oncoprotein. hdm2 binds to the N-terminal transactivation domain of p53 to block the transcriptional activity of p53 directly. hdm2 also functions as the E3 ligase that ubiquitinates p53 for proteasome degradation. Fluorescence anisotropy was employed to measure directly the binding of hdm2(1-126) to a p53 N-terminal peptide labeled with Oregon Green (an analogue of fluorescein). Phosphorylation of Ser15 and Ser2O did not affect the binding of the p53 peptide to hdm2. Thrl8 phosphorylation, on the other hand, reduced the binding by at least 20-fold. This suggests that phosphorylation of Thr18 could be a regulatory mechanism that disrupts the hdm2-p53 complex, thus activating p53 in response to DNA damage. The effect of p53 peptide length on binding to hdm2 was also measured quantitatively. Interestingly, p53(18-26) exhibits 10-fold higher affinity to hdm2 than do longer peptides (20- or 35-mer). This result may reflect a strong entropic barrier to binding for the longer peptides.

Optical mapping of BAC clones from the human Y chromosome DAZ locus

The accurate mapping of clones derived from genomic regions containing complex arrangements of repeated elements presents special problems for DNA sequencers. Recent advances in the automation of optical mapping have enabled us to map a set of 16 BAC clones derived from the DAZ locus of the human Y chromosome long arm, a locus in which the entire DAZ gene as well as subsections within the gene copies have been duplicated. High-resolution optical mapping employing seven enzymes places these clones into two contigs representing four distinct copies of the DAZ gene and highlights a number of differences between individual copies of DAZ.