A detailed investigation of two cases exhibiting characteristics of the 6p deletion syndrome

Deletions of the short arm of chromosome 6 are relatively rare, only 16 cases having been described in the literature so far. Here we present a detailed investigation by fluorescence in situ hybridisation of two further cases with different but overlapping interstitial deletions involving 6p22, 6p23 and 6p24. The main features involved are craniofacial malformations, heart and kidney defects, mental retardation/developmental delay, hypotonia and hydrocephalus. By using 36 yeast artificial chromosome and cosmid clones from a contig covering 6p22.3–6p25 and other probes with defined cytogenetic locations within 6p21– 6p22 we have precisely localised the breakpoints involved in each of the cases, estimated the sizes of the deleted regions and defined the region that is hemizygously deleted in both cases. Received: 20 March 1996 / Revised: 13 May 1996     

Delineation of the critical deletion region for congenital heart defects, on chromosome 8p23.1

Deletions in the distal region of chromosome 8p (del8p) are associated with congenital heart malformations. Other major manifestations include microcephaly, intrauterine growth retardation, mental retardation, and a characteristic hyperactive, impulsive behavior. We studied genotype-phenotype correlations in nine unrelated patients with a de novo del8p, by using the combination of classic cytogenetics, FISH, and the analysis of polymorphic DNA markers. With the exception of one large terminal deletion, all deletions were interstitial. In five patients, a commonly deleted region of approximately 6 Mb was present, with breakpoints clustering in the same regions. One patient without a heart defect or microcephaly but with mild mental retardation and characteristic behavior had a smaller deletion within this commonly deleted region. Two patients without a heart defect had a more proximal interstitial deletion that did not overlap with the commonly deleted region. Taken together, these data allowed us to define the critical deletion regions for the major features of a del8p.     

Contiguous deletion syndromes.

In the past few years, clinical, cytogenetic and molecular analysis of patients with complex phenotypes has led to the identification of syndromes caused by deletions of adjacent disease genes on a chromosome. These conditions, referred to as contiguous deletion syndromes, are an important component of the syndromes recognized in medical genetics, and the DNA from patients affected by these disorders is useful for the mapping and cloning of disease genes.     

Interstitial deletion 13q syndromes: A report on two unrelated patients

Summary A partial monosomy 13 by interstitial deletion was found in the complement of two patients with mental retardation and mild dysmorphic features. Neither of the patients had a retinoblastoma, even though the second patient had a 13q14 deletion. The karyotype-phenotype correlation in the two patients suggests the need to reconsider the clinical profile of these rare chromosomal syndromes in a large series of subjects.     

Yeast oligosaccharyltransferase consists of two functionally distinct sub-complexes, specified by either the Ost3p or Ost6p subunit

The key step of N-glycosylation of proteins in the endoplasmic reticulum is catalyzed by the hetero-oligomeric protein complex oligosaccharyltransferase (OST). It transfers the lipid-linked core-oligosaccharide to selected Asn-X-Ser/Thr-sequences of nascent polypeptide chains. Biochemical and genetic approaches have revealed that OST from Saccharomyces cerevisiae consists of nine subunits: Wbp1p, Swp1p, Stt3p, Ost1p, Ost2p, Ost4p, Ost5p, Ostp3 and Ost6p. By blue native polyacrylamide electrophoresis we show that yeast OST consists of two isoforms with distinct functions differing only in the presence of the two related Ost3 and Ost6p proteins. The OST6-complex was found to be important for cell wall integrity and temperature stress. Ost3p and Ost6p are not essential for OST activity, and can in part displace each other in the complex when overexpressed, suggesting a dynamic regulation of the complex formation.     

Partial deletion 10p syndrome. Report of two patients.

Two patients with partial deletion of the short arm of chromosome 10 are described. They showed most of the features observed in twenty other known patients, including growth retardation, mental deficiency, abnormally shaped skull, distinct facial dysmorphisms, cardiac and genitourinary malformations, and limbs anomalies. One of our patients also had features of the DiGeorge sequence, which has been found in five other cases with this imbalance.     

Delineation of immunologically and biochemically distinct HLA-A2 antigens

Cytotoxic T cell (CTL) recognition of influenza virus in conjunction with HLA-A2 was examined in a population study. Virus-infected target cells from three unrelated A2-positive donors were not lysed by virus-immune CTL from any donor matched only for A2. The A2 antigens of these three donors were indistinguishable from the A2 antigens of other A2-positive donors as assessed by extensive serologic analyses; however, isoelectric focusing (IEF) of A2 molecules from these three donors demonstrated that their A2 heavy polypeptide chains are structurally distinct from those of "normal" A2-positive donors. To date 11% of all A2-positive donors tested exhibited a "variant" A2-associated CTL restriction antigen, and IEF of A2 heavy chains from all "variant" A2-positive cells revealed structural differences in each of these polypeptides. These results suggest there may be considerably greater polymorphism of HLA-A gene products than has been revealed by current serologic techniques.     

Mdmx stabilizes p53 and Mdm2 via two distinct mechanisms

The p53 protein maintains genomic integrity through its ability to induce cell cycle arrest or apoptosis in response to various forms of stress. Substantial regulation of p53 activity occurs at the level of protein stability, largely determined by the activity of the Mdm2 protein. Mdm2 targets both p53 and itself for ubiquitylation and subsequent proteasomal degradation by acting as an ubiquitin ligase, a function that needs an intact Mdm2 RING finger. For efficient degradation of p53 nuclear export appears to be required. The Mdmx protein, structurally homologous to Mdm2, does not target p53 for degradation, but even stabilizes both p53 and Mdm2, an activity most likely mediated by heterodimerization of the RING fingers of Mdm2 and Mdmx. Here we show that Mdmx expression leads to accumulation of ubiquitylated, nuclear p53 but does not significantly affect the Mdm2-mediated ubiquitylation of p53. In contrast, Mdmx stabilizes Mdm2 by inhibiting its self-ubiquitylation.     

Acrocentric/18p translocation in two mentally retarded males. Delineation of the adult phenotype

In this report we describe two adult male patients with a chromosomal rearrangement involving the short arm of chromosome 18 and an acrocentric chromosome. In addition to moderate mental retardation and verbal disability they presented dysmorphic stigmata similar to those found in the Noonan syndrome.     

Yeast Pex14p possesses two functionally distinct Pex5p and one Pex7p binding sites

Current evidence favors a cycling receptor model for the import of peroxisomal matrix proteins. The yeast Pex14 protein together with Pex13p and Pex17p form the docking subcomplex at the peroxisomal membrane and interact in this cycle with both soluble import receptors Pex5p and Pex7p. In a first step of a structure-function analysis of Saccharomyces cerevisiae Pex14p, we mapped its binding sites with both receptors. Using the yeast two-hybrid system and pull-down assays, we showed that Pex5p directly interacts with two separate regions of ScPex14p, amino acid residues 1-58 and 235-308. The latter binding site at the C terminus of ScPex14p overlaps with a binding site of Pex7p at amino acid residues 235-325. The functional assessment of these two binding sites of ScPex14p with the peroxisomal targeting signal receptors indicates that they have distinct roles. Deletion of the N-terminal 58 amino acids caused a partial defect of matrix protein import in pex14delta cells expressing the Pex14-(59-341)-p fragment; however, it did not lead to a pex phenotype. In contrast, truncation of the C-terminal 106 amino acids of ScPex14p completely blocked this process. On the basis of these and other published data, we propose that the C terminus of Pex14p contains the actual docking site and discuss the possibility that the N terminus could be involved in a Pex5p-Pex14p association inside the peroxisomal membrane.     

Sir2p exists in two nucleosome-binding complexes with distinct deacetylase activities

The absolute requirement for the histone deacetylase activity of Sir2p in silencing coupled with the conservation of Sir2p-like proteins in larger eukaryotes suggests that this molecule plays an important role in gene regulation in all organisms. Here we report the purification and characterization of two Sir2p-containing protein complexes; one of which contains Sir4p and the other Net1p. The Sir4p-containing complex has an NAD-dependent histone deacetylase activity, while the Net1p-containing complex possesses deacetylase activity but only weak NAD-dependent histone deacetylase activity. Finally, we demonstrate that the Sir2p-containing complexes bind nucleosomes efficiently and partially restrict accessibility of the linker DNA to enzymatic probes.     

Members of the S100 family bind p53 in two distinct ways

p53 binds to some members of the S100 family (S100B, S100A4, S100A2, and S100A1). We previously showed that both S100B and S100A4 bind to the p53 tetramerization domain, and consequently control its oligomerization state, but only S100B binds to the C-terminal negative regulatory domain (NRD). Here, we investigate other binding partners for p53 within the S100 family (S100A6 and S100A11), and show that binding to the p53 tetramerization domain seems to be a general feature of the S100 family, while binding to the NRD is a characteristic of a subset of the family.     

The ScPex13p SH3 domain exposes two distinct binding sites for Pex5p and Pex14p

Pex13p is an essential component of the peroxisomal protein import machinery and interacts via its C-terminal SH3 domain with the type II SH3-ligand Pex14p and the non-PXXP protein Pex5p. We report the solution structure of the SH3 domain of Pex13p from Saccharomyces cerevisiae and the identification of a novel-binding pocket, which binds a non-PXXP-peptide representing the binding site of Pex5p. Chemical shift assays revealed the binding sites for Pex5p and Pex14p ligand peptides to be distinct and spatially separated. Competition assays demonstrated that the two ligand peptides can bind simultaneously to the SH3 domain.     

High-risk human papillomavirus E6 protein has two distinct binding sites within p53, of which only one determines degradation.

Human papillomavirus (HPV) E6 protein can inactivate tumor suppressor p53 by inducing its degradation. We now find that high-risk HPV E6 binds to p53 at two distinct sites; one is within the core structure of p53, and another is at the C terminus of p53. Binding to the core of p53 is required for E6-mediated degradation, as shown by deletion analysis and the properties of a point mutant at residue 135. Both low- and high-risk HPV E6 can bind to a C-terminal region of p53, but these interactions do not induce degradation. These results resolve previous seemingly contradictory findings that attributed the distinctive functional properties of high- and low-risk E6 proteins to either a difference in their abilities to associate with p53 or a difference in their N-terminal structures.     

Delineation of ecologically distinct units of marine Bacteroidetes in the Northwestern Mediterranean Sea

Bacteroidetes is one of the dominant phyla of ocean bacterioplankton, yet its diversity and population structure is poorly understood. To advance in the delineation of ecologically meaningful units within this group, we constructed near full‐length 16S rRNA gene clone libraries from contrasting marine environments in the NW Mediterranean. Based on phylogeny and the associated ecological variables (depth and season), 24 different Bacteroidetes clades were delineated. By considering their relative abundance (from iTag amplicon sequencing studies), we described the distribution patterns of each of these clades, delimiting them as Ecologically Significant Taxonomic Units (ESTUs). Spatially, there was almost no overlap among ESTUs at different depths. In deep waters there was predominance of Owenweeksia, Leeuwenhoekiella, Muricauda‐related genera, and some depth‐associated ESTUs within the NS5 and NS2b marine clades. Seasonally, multi‐annual dynamics of recurring ESTUs were present with dominance of some ESTUs within the NS4, NS5 and NS2b marine clades along most of the year, but with variable relative frequencies between months. A drastic change towards the predominance of Formosa‐related ESTUs and one ESTU from the NS5 marine clade was typically present after the spring bloom. Even though there are no isolates available for these ESTUs to determine their physiology, correlation analyses identified the environmental preference of some of them. Overall, our results suggest that there is a high degree of niche specialisation within these closely related clades. This work constitutes a step forward in disentangling the ecology of marine Bacteroidetes, which are essential players in organic matter processing in the oceans.