Altered DNA ligase I activity in Bloom's syndrome cells

Cells from patients with Bloom's syndrome, a rare disease associated with increased cancer frequency, exhibit cytological abnormalities. These include increased numbers of homologous chromatid interchange figures and sister-chromatid exchanges, together with abnormally slow replicon-fork progression and retarded rate of DNA-chain maturation, and suggest that the primary defect in this recessive disorder affects S-phase DNA replication. DNA ligases and DNA polymerases have long been prime candidates for abnormality in Bloom's syndrome, but various studies of DNA polymerases in Bloom's syndrome cells have disclosed no abnormalities. Evidence is presented here, as in the accompanying paper from a different laboratory, for the existence in Bloom's syndrome of an abnormality of the DNA ligase involved in semi-conservative DNA replication.