DNA ligase I found in nucleus and mitochondria%3B essential enzyme that joins Okazaki fragments during DNA replication%3B also acts in ribonucleotide excision repair%2C base excision repair%2C and recombination%3B DNA ligase I mutants trigger ubiquitination of PCNA at K107%2C facilitating Rad59p-mediated bypass of unligated Okazaki fragments%3B human homolog LIG1 can complement yeast cdc9 temperature-sensitive mutant at restrictive temperature