Fluorescence in situ hybridization with a synthetic (T2AG3)n polynucleotide detects several intrachromosomal telomere-like repeats on human chromosomes

(T2AG3) repeats comprise the telomeres of human chromosomes and also are present at interstitial locations. Using a long synthetic (T2AG3)n probe, we have localized telomere-like repeats at several internal sites on human chromosomes.

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.

SPECIFICITY OF POTASSIUM-ACTIVATED PHOSPHODIESTERASE OF ESCHERICHIA COLI

A potassium-activated phosphodiesterase that hydrolyzes polyribonucleotides to 5'-mononucleotides has been purified approximately 600-fold from extracts of Escherichia coli B. The purified enzyme appears to be specific for single-stranded polyribonucleotides: helical forms are not hydrolyzed, nor do they inhibit the hydrolysis of single-stranded chains.