D21S215 is a (GT)n polymorphic marker close to centromeric alphoid sequences on chromosome 21.

A plasmid, AWZ1, that contained a dinucleotide (GT)n repeat was identified from a chromosome 21-specific genomic library. When amplified by PCR from human genomic DNA, the repeat length was highly polymorphic between individuals; its location, D21S215, was mapped in the CEPH pedigrees by linkage analysis to the pericentromeric region of chromosome 21. It is the closest polymorphic marker to alphoid sequences on this chromosome.     

Characterisation of three microsatellite polymorphisms (D21S1262, D21S1419 and D21S1421) from band 21q22.1

We have isolated three clones, containing highly polymorphic CA-repeat sequences, from a human chromosome 21 phage library (LA21NS01). These clones have been localised to band q22.1 by using a chromosome 21 somatic cell hybrid panel. D21S1262 is located between breakpoints 6918-8a1 and 32S, and D21S1419 and D21S1421 are localised between breakpoints JC6-A and MRC2G. Their observed heterozygosities range between 0.75 and 0.85 as shown by unrelated reference parents from the Centre d'Etude du Polymorphisme Humain. These highly polymorphic markers should be useful for improving the analysis of this region of chromosome 21, which contains important genes such as SOD1, GART and IFNAR.     

Linkage of DNA probe B79a (D7S13) to cystic fibrosis

We have conducted, in 64 affected families, a study of linkage between the anonymous DNA segment pB79a (D7S13) and the locus for cystic fibrosis (CF) on chromosome 7q. The maximum lod score was 12.60 at theta = .08 (confidence bounds .045-.135). Although D7S13 is not sufficiently close to CF for routine use in DNA-based prenatal diagnosis, it will be helpful in certain families when other nearby markers are uninformative. D7S13 will also be useful for refining the linkage map of the CF region.     

Walking, cloning, and mapping with yeast artificial chromosomes: a contig encompassing D21S13 and D21S16.

Chromosome 21 has often been used as a model system for the development of genome mapping and cloning strategies in humans. In this report methods for systematic chromosome walking, cloning, and mapping are exemplified in the construction of a 1.5-Mb yeast artificial chromosome (YAC) contig encompassing and extending 400 kb beyond each of the genetic loci D21S13 and D21S16. Isolation of insert-terminal sequences from YACs in this contig provides a set of closely spaced physical markers. These have been used to generate a long-range genomic restriction map.     

The yeast 8-oxoguanine DNA glycosylase (Ogg1) contains a DNA deoxyribophosphodiesterase (dRpase) activity.

The yeast OGG1 gene was recently cloned and shown to encode a protein that possesses N-glycosylase/AP lyase activities for the repair of oxidatively damaged DNA at sites of 7,8-dihydro-8-oxoguanine (8-oxoguanine). Similar activities have been identified for Escherichia coli formamidopyrimidine-DNA glycosylase (Fpg) and Drosophila ribosomal protein S3. Both Fpg and S3 also contain a deoxyribophosphodiesterase (dRpase) activity that removes 2-deoxyribose-5-phosphate at an incised 5' apurinic/apyrimidinic (AP) sites via a beta-elimination reaction. Drosophila S3 also has an additional activity that removes trans-4-hydroxy-2-pentenal-5-phosphate at a 3' incised AP site by a Mg2+-dependent hydrolytic mechanism. In view of the substrate similarities between Ogg1, Fpg and S3 at the level of base excision repair, we examined whether Ogg1 also contains dRpase activities. A glutathione S-transferase fusion protein of Ogg1 was purified and subsequently found to efficiently remove sugar-phosphate residues at incised 5' AP sites. Activity was also detected for the Mg2+-dependent removal of trans -4-hydroxy-2-pentenal-5-phosphate at 3' incised AP sites and from intact AP sites. Previous studies have shown that DNA repair proteins that possess AP lyase activity leave an inefficient DNA terminus for subsequent DNA synthesis steps associated with base excision repair. However, the results presented here suggest that in the presence of MgCl2, Ogg1 can efficiently process 8-oxoguanine so as to leave a one nucleotide gap that can be readily filled in by a DNA polymerase, and importantly, does not therefore require additional enzymes to process trans -4-hydroxy-2-pentenal-5-phosphate left at a 3' terminus created by a beta-elimination catalyst.     

Linkage mapping of the highly informative DNA marker D21S156 to human chromosome 21 using a polymorphic GT dinucleotide repeat

A (GT)n repeat within the anonymous DNA sequence D21S156 was shown to be highly polymorphic in DNA from members of the 40 CEPH families. At least 12 alleles of this locus were recognized by electrophoresis on polyacrylamide gels of DNA amplified by the polymerase chain reaction (PCR) using primers flanking the (GT)n repeat. The polymorphism information content was 0.82. PCR amplification of DNA from somatic cell hybrid lines mapped D21S156 to human chromosome 21 and linkage analysis localized this marker close to the loci ETS2, D21S3, and HMG14 on chromosomal band 21q22.3. This polymorphism is highly informative and can serve as an anchor locus for human chromosome 21.     

Identification of two highly polymorphic CA-repeats (D21S1224 and D21S1261) on human chromosome 21q22.3

Two highly polymorphic CA-repeat microsatellites (D21S1224 and D21S1261) are reported. The clones containing these CA-repeats (ABM-C60 and ABM-C29) have been isolated from a human chromosome-21-specific library (LA21NS01) and have been localised to the q22.3 band using a specific chromosome 21 somatic cell hybrid panel. Both polymorphisms showed heterozygosities of 0.83 in the unrelated reference parents from the Centre d'Etude du Polymorphisme Humain. These new markers should improve the map of the 21q22.3 region, which is believed to contain a large number of genes.     

A new EcoRI polymorphism at the D21S13 locus

Summary The D21S13 locus has shown linkage to a gene for familial Alzheimer disease (FAD) on chromosome 21 (St. George-Hyslop et al. 1987). The limited informativeness of probes for this locus have hindered precise mapping of the FAD locus and analysis of nonallelic heterogeneity in FAD (Schellenberg et al. 1988; St. George-Hyslop et al. 1987). We describe a new EcoRI polymorphism at the D21S13 locus that may be useful for the further study of FAD families.