ABSTRACT
Trinucleotide repeat (TNR) instability can cause a variety of human genetic diseases including myotonic dystrophy and Huntington's disease. Recent genetic data show that instability of the CAG/CTG repeat DNA is dependent on its length and replication origin. In yeast, the RAD27 (human FEN-1 homologue) null mutant has a high expansion frequency at the TNR loci. We demonstrate here that FEN-1 processes the 5'-flap DNA of CTG/CAG repeats, which is dependent on the length in vitro. FEN-1 protein can cleave the 5'-flap DNA containing triplet repeating sequence up to 21 repeats, but the activity decreases with increasing size of flap above 11 repeats. In addition, FEN-1 processing of 5'-flap DNA depends on sequence, which play a role in the replication origin-dependent TNR instability. Interestingly, FEN-1 can cleave the 5'-flap DNA of CTG repeats better than CAG repeats possibly through the flap-structure. Our biochemical data of FEN-1's activity with triplet repeat DNA clearly shows length dependence, and aids our understanding on the mechanism of TNR instability.
Subject(s)
Humans , Base Sequence , DNA, Single-Stranded/metabolism , Endodeoxyribonucleases/genetics , Flap Endonucleases , Gene Expression Regulation , Genetic Diseases, Inborn/genetics , Nucleic Acid Conformation , Trinucleotide Repeat Expansion , Trinucleotide RepeatsABSTRACT
Trinucleotide repeat (TNR) instability can cause a variety of human genetic diseases including myotonic dystrophy and Huntington's disease. Recent genetic data show that instability of the CAG/CTG repeat DNA is dependent on its length and replication origin. In yeast, the RAD27 (human FEN-1 homologue) null mutant has a high expansion frequency at the TNR loci. We demonstrate here that FEN-1 processes the 5'-flap DNA of CTG/CAG repeats, which is dependent on the length in vitro. FEN-1 protein can cleave the 5'-flap DNA containing triplet repeating sequence up to 21 repeats, but the activity decreases with increasing size of flap above 11 repeats. In addition, FEN-1 processing of 5'-flap DNA depends on sequence, which play a role in the replication origin-dependent TNR instability. Interestingly, FEN-1 can cleave the 5'-flap DNA of CTG repeats better than CAG repeats possibly through the flap-structure. Our biochemical data of FEN-1's activity with triplet repeat DNA clearly shows length dependence, and aids our understanding on the mechanism of TNR instability.
Subject(s)
Humans , Base Sequence , DNA, Single-Stranded/metabolism , Endodeoxyribonucleases/genetics , Flap Endonucleases , Gene Expression Regulation , Genetic Diseases, Inborn/genetics , Nucleic Acid Conformation , Trinucleotide Repeat Expansion , Trinucleotide RepeatsABSTRACT
OBJECTIVE: To evaluate factor XII deficiency in patients with recurrent spontaneous abortion and its relation to aPTT. MATERIAL AND METHOD: Factor XII was analyzed by clotting method. RESULTS: Of 70 patients with recurrent spontaneous abortion, there were 35 cases of factor XII deficiency. Among them, there were only 3 cases of prolonged aPTT. CONCLUSIONS: It is still unclear whether factor XII deficiency is related to recurrent spontaneous abortion. Molecular approaches should be used to understand further the causal relationship. But based on this result, in the workup of patients with recurrent spontaneous abortion, factor XII should be included. aPTT is not likely to represent the abnormality of factor XII.