Localization of an ataxia-telangiectasia locus to a 3-cM interval on chromosome 11q23: Linkage analysis of 111 families by an international consortium

Linkage of at least two complementation groups of ataxia-telangiectasia (AT) to the chromosomal region 11q23 is now well established. We provide here an 18-point map of the surrounding genomic region, derived from linkage analysis of 40 CEPH families. On the basis of this map, 111 AT families from Turkey, Israel, England, Italy, and the United States were analyzed, localizing the AT gene(s) to an 8-cM sex-averaged interval between the markers STMY and D11S132/NCAM. A new Monte Carlo method for computing approximate location scores estimates this location as being at least 10(8) times more likely than the next most likely interval, with a support interval midway between STMY and D11S132 that is either 5.2 cM (sex-averaged and conservatively based on 3 lod scores from the maximum-location score) or 2.8 cM (male specific, based on a 2.72:1 interval-specific female-to-male distance ratio.     

Ataxia-telangiectasia: linkage analysis of chromosome 11q22-23 markers in Turkish families.

To further pinpoint the location of the genes for ataxia-telangiectasia on the long arm of chromosome 11, we performed linkage analysis and analysis of recombinants of genetic haplotypes on 14 Turkish families with ataxia-telangiectasia, 12 of which were consanguineous. These studies used more than 25 polymorphic genetic markers spanning a region of the long arm of chromosome 11 that is larger than 50 cM. Seven markers gave significant LOD scores to AT: CJ5, DRD2, CJ208, S144, CD3E, PBGD, and S147, as did haplotypes created with pairs of markers DRD2/CJ5 and S144/CJ208, giving recombination fractions (theta) of 0.00, 0.00, 0.05, 0.08, 0.03, 0.09, 0.07, 0.00, and 0.06, respectively. Monte Carlo analysis of these 14 Turkish families indicated the best location for a single AT gene to be within a 6 cM sex-averaged (3 cM male-specific) interval defined by STMY and CJ77; this was three times more likely than the next most likely location (peak III) at the DRD2 locus. The analysis also revealed a peak (peak II) between S147 and S133, which may represent the complementation group D gene. Recombinant analysis of haplotypes also localized an AT locus to the STMY-CJ77 interval. Taken together, these results suggest that at least two distinct AT loci exist (ATA and ATD) at 11q22-23, with perhaps a third locus, ATC, located very near to the ATA gene. This genetic heterogeneity further complicates plans to isolate the major ATA and ATC genes and to begin identifying AT carriers in the general population.     

DNA analysis in Turkish Duchenne/Becker muscular dystrophy families

Summary The molecular genetics of Duchenne/Becker muscular dystrophy was investigated in 81 affected Turkish families. Deletions were detected by multiplex polymerase chain reaction assays and cDNA Southern analyses. The distribution of the deletions along the gene and their correlation to clinical phenotype were different from the studies reported on other populations. Moreover, DNA polymorphisms in mothers were determined using 8 DNA probes and three CA repeat sequences, and a high degree of informativeness was observed.     

Dinucleotide repeat polymorphism at 11q23

A highly polymorphic CA repeat sequence was identified near the NCAM gene on chromosome 11q23. It should be a useful marker in the localization of genes responsible for neurological disorders that are known to map to this region.     

Methionine-enkephalin peptides in human teeth

The presence of the free opioid pentapeptide methionine enkephalin (ME) and of ME-containing peptide(s) was established firmly in decalcified, depulped human teeth by using a combination of methods including RP-HPLC, radioimmunoassay, radioreceptorassay, trypsin, carboxypeptidase B, fast atom bombardment mass spectrometry, and MS/MS methodology. Positive structural identification of ME was made with mass spectrometry. Those data demonstrate the presence of the preproenkephalinergic A system in the human trigeminal sensory termini.     

Separation of the minimal replication region of the F plasmid into a replication origin segment and a trans-acting segment

Summary An analysis was carried out on the replication functions within a 2.3 kilobase (kb) segment of the F plasmid which contains an origin (ori S) of replication and is capable of autonomous replication inEscherichia coli. Two separable regions were delineated for this segment: an origin region of approximately 1,140 bp in length and a segment of approximately 1,400 bp that functionsin trans to support replication of the origin region. The trans-acting segment is functional as part of an F replicon or when inserted into theE. coli chromosome. A prominent feature of the trans-acting segment is a coding sequence for a 29 K protein (Murotsu et al. 1981).     

The killing of African trypanosomes by ethidium bromide

Introduced in the 1950s, ethidium bromide (EB) is still used as an anti-trypanosomal drug for African cattle although its mechanism of killing has been unclear and controversial. EB has long been known to cause loss of the mitochondrial genome, named kinetoplast DNA (kDNA), a giant network of interlocked minicircles and maxicircles. However, the existence of viable parasites lacking kDNA (dyskinetoplastic) led many to think that kDNA loss could not be the mechanism of killing. When recent studies indicated that kDNA is indeed essential in bloodstream trypanosomes and that dyskinetoplastic cells survive only if they have a compensating mutation in the nuclear genome, we investigated the effect of EB on kDNA and its replication. We here report some remarkable effects of EB. Using EM and other techniques, we found that binding of EB to network minicircles is low, probably because of their association with proteins that prevent helix unwinding. In contrast, covalently-closed minicircles that had been released from the network for replication bind EB extensively, causing them, after isolation, to become highly supertwisted and to develop regions of left-handed Z-DNA (without EB, these circles are fully relaxed). In vivo, EB causes helix distortion of free minicircles, preventing replication initiation and resulting in kDNA loss and cell death. Unexpectedly, EB also kills dyskinetoplastic trypanosomes, lacking kDNA, by inhibiting nuclear replication. Since the effect on kDNA occurs at a >10-fold lower EB concentration than that on nuclear DNA, we conclude that minicircle replication initiation is likely EB's most vulnerable target, but the effect on nuclear replication may also contribute to cell killing.     

Details of ssDNA annealing revealed by an HSV-1 ICP8–ssDNA binary complex

Infected cell protein 8 (ICP8) from herpes simplex virus 1 was first identified as a single-strand (ss) DNA-binding protein. It is essential for, and abundant during, viral replication. Studies in vitro have shown that ICP8 stimulates model replication reactions, catalyzes annealing of complementary ssDNAs and, in combination with UL12 exonuclease, will catalyze ssDNA annealing homologous recombination. DNA annealing and strand transfer occurs within large oligomeric filaments of ssDNA-bound ICP8. We present the first 3D reconstruction of a novel ICP8–ssDNA complex, which seems to be the basic unit of the DNA annealing machine. The reconstructed volume consists of two nonameric rings containing ssDNA stacked on top of each other, corresponding to a molecular weight of 2.3 MDa. Fitting of the ICP8 crystal structure suggests a mechanism for the annealing reaction catalyzed by ICP8, which is most likely a general mechanism for protein-driven DNA annealing.     

The Werner syndrome protein binds replication fork and holliday junction DNAs as an oligomer

Werner syndrome is an inherited disease displaying a premature aging phenotype. The gene mutated in Werner syndrome encodes both a 3' --> 5' DNA helicase and a 3' --> 5' DNA exonuclease. Both WRN helicase and exonuclease preferentially utilize DNA substrates containing alternate secondary structures. By virtue of its ability to resolve such DNA structures, WRN is postulated to prevent the stalling and collapse of replication forks that encounter damaged DNA. Using electron microscopy, we visualized the binding of full-length WRN to DNA templates containing replication forks and Holliday junctions, intermediates observed during DNA replication and recombination, respectively. We show that both wild-type WRN and a helicase-defective mutant bind with exceptionally high specificity (>1000-fold) to DNA secondary structures at the replication fork and at Holliday junctions. Little or no binding is observed elsewhere on the DNA molecules. Calculations of the molecular weight of full-length WRN revealed that, in solution, WRN exists predominantly as a dimer. However, WRN bound to DNA is larger; the mass is consistent with that of a tetramer.