3 ARS ELEMENTS CONTRIBUTE TO THE URA4-REPLICATION ORIGIN REGION IN THE FISSION YEAST, SCHIZOSACCHAROMYCES-POMBE

The ura4 replication origin region, which is located near the ura4 gen e on chromosome III of the fission yeast, Schizosaccharomyces pombe, c ontains multiple initiation sites. We have used 2D gel electrophoretic replicon mapping methods to study the distribution of these initiatio n sites, and have found that they are concentrated near three ARS elem ents (stretches of DNA which permit autonomous plasmid replication). T o determine the roles of these ARS elements in the function of the ura 4 origin region, we deleted either one or two of them from the chromos ome and then assessed the consequences of the deletions by 2D gel elec trophoresis. The results suggest that each of the three ARS elements i s responsible for the initiation events in its vicinity and that the A RS elements interfere with each other in a hierarchical fashion. It is possible that the large initiation zones of animal cells are similarl y composed of multiple mutually interfering origins.