title: Methylation is co-ordinated on the putative replication origins of Physarum ribosomal DNA.
abstract: In Physarum polycephalum, the ribosomal DNA is found as 60,000 base-pair palindromes. Each rDNA has four symmetrically arranged replication origins flanked by ribosomal RNA genes. A particular sequence, the putative replication origin, is repeated at the approximate position of each origin and nowhere else in the molecule. On a typical rDNA molecule, only one origin is active per replication cycle. We show that both the level and co-ordination of methylation result in asymmetrically methylated rDNA molecules that are particularly hypomethylated at one of their four putative replication origins. This pattern of methylation on a typical rDNA molecule is consistent with a model where hypomethylation is a determinant of origin activity.
authors.affiliation: Department of Biological Chemistry, School of Medicine, University of California, Davis 95616.
authors.forename: C A
authors.initials: CA
authors.lastname: Cooney
authors.forename: R L
authors.initials: RL
authors.lastname: Eykholt
authors.forename: E M
authors.initials: EM
authors.lastname: Bradbury
mesh_terms: D002453:Cell Cycle; D004261:DNA Replication; D004271:DNA, Fungal / Q000235:genetics / Q000378:metabolism; D004275:DNA, Ribosomal / Q000235:genetics* / Q000378:metabolism; D003841:Deoxycytidine / Q000031:analogs & derivatives / Q000235:genetics / Q000378:metabolism; D005800:Genes, Fungal; D008745:Methylation; D010804:Physarum / Q000201:enzymology / Q000235:genetics*
chemical_list: D004271:DNA, Fungal; D004275:DNA, Ribosomal; D003841:Deoxycytidine; C016569:5-methyldeoxycytidine