A DNA-REPLICATION ENHANCER IN SACCHAROMYCES-CEREVISIAE

We have dissected the autonomously replicating sequence ARS121 using site-directed in vitro mutagenenis. Three domains important for origin function were identified; one of these is essential and contains an 11-base-pair sequence resembling the canonical ARS core consensus; the second region, deletion of which affects the efficiency of the origin, is located 3′ to the T-rich strand of the essential sequence and encompasses several elements with near matches It the ARS core consensus; the third region, containing two BF1 DNA-binding sites and located 5′ to the essential sequence, also affects the efficiency of the ARS. Here we demstrate that a synthetic OBF1 DNA-binding site can substitute for the entire third domain in origin function. A dimer of the synthetic binding site, fused to a truncated origin containing domains one and two, restored the origin activity to the levels of the wild-type ARS. The stimulation of origin function by the synthetic binding site was relatively orientation independent and could occur at distances as far as 1 kilobase upstream to the essential domain. Based on these results we conclude that the OBF1 DNA-binding site is an enhancer of DNA replication. We suggest that the DNA-binding site and the OBF1 protein are involved in the regulation of the activation of nuclear origins of replication in Saccharomyces cerevisiae.