DNA repair in a yeast origin of replication: contributions of photolyase and nucleotide excision repair

DNA damage formation and repair are tightly linked to protein-DNA interacti ons in chromatin. We have used minichromosomes in yeast as chromatin substr ates in vivo to investigate how nucleotide excision repair (NER) and repair by DNA-photolyase (photoreactivation) remove pyrimidine dimers from an ori gin of replication (ARSI). The ARSI region is nuclease sensitive and flanke d by nucleosomes on both sides. Photoreactivation was generally faster than NER at all sites. Site-specific heterogeneity of repair was observed for b oth pathways. This heterogeneity was different for NER and photoreactivatio n and it was altered in a minichromosome where ARS1 was transcribed. The re sults indicate distinct interactions of the repair systems with protein com plexes bound in the ARS region (ORC, Abf1) and a predominant role of photol yase in CPD repair of an origin of replication.