The Replication of Ribosomal DNA in Physarum polycephalum

Abstract

The DNA coding for ribosomal RNA in P. polycephalum exists as a collection of extra-chromosomal molecules of MW 37 .times. 106. The replication of rDNA was investigated with the following results. Replication of rDNA is unscheduled meaning that molecules that are replicated at any particular time in 1 mitotic cycle have an equal probability of replicating again in each time interval in the subsequent cycle. Similarly, in a single cycle, some molecules replicate more than once, and some not at all. Replication forks appear to move bidirectionally from points 45% or 33% from one end of the DNA. Replicating molecules observed by EM are all linear.