The major DNA ligase activity in proliferating mammalian cells is due to the high molecular weight enzyme designated DNA ligase I. Barnes et al. (1990) cloned cDNA for human DNA ligase I, both by functional complementation of a Saccharomyces cerevisiae cdc9 mutation and by hybridization with oligonucleotide probes corresponding to peptide sequences of the purified bovine enzyme. Hybridization between the cloned sequences and mRNA as well as genomic DNA indicated that the human enzyme is transcribed from a single-copy gene.

Barnes et al. (1990) mapped the DNA ligase I gene to chromosome 19 by hybridization to DNAs from well-characterized rodent-human somatic cell hybrids retaining subsets of human chromosomes.