INITIATION AT CLOSELY SPACED REPLICATION ORIGINS IN A YEAST CHROMOSOME

Replication of eukaryotic chromosomes involves initiation at origins s paced an average of 50 to 100 kilobase pairs. In yeast, potential orig ins can be recognized as autonomous replication sequences (ARSs) that allow maintenance of plasmids. However, there are more ARS elements th an active chromosomal origins. The possibility was examined that close spacing of ARSs can lead to inactive origins. Two ARSs located 6.5 ki lobase pairs apart can indeed interfere with each other. Replication i s initiated from one or the other ARS with equal probability, but rare ly (<5%) from both ARSs on the same DNA molecule.