LENGTH OF RNA TRANSCRIBED ON REPLICATIVE FORM DNA OF COLIPHAGE FD

The length of RNA synthesized on the doubly-closed replicative form DNA of coliphage fd was determined based on the fact that the RNA chains were initiated predominantly with purine nucleotides. Using a purified Escherichia coli RNA polymerase and RF-I DNA† † Abbreviation used: RF-I DNA, doubly-closed replicative form DNA., RNA was synthesized in reaction mixtures containing either [γ-32P]ATP or [γ-32P]GTP, and analysed by band centrifugation. The sedimentation profile of RNA labelled with [γ-32P]GTP showed principally two 32P peaks of about 12 and 17 s. In contrast, RNA labelled with [γ-32P]ATP produced only a major 32P peak of about 26 s. When the reaction mixtures were analysed directly before deproteinization, the indicated RNA components appeared apart from the DNA-RNA-enzyme complex. From the ratio of 3H incorporated into RNA to 32P of the initiator nucleotides, molecular weights of the 12, 17 and 26 s RNA's were estimated to be about 4.5 × 105, 6.2 × 105 and 1.3 × 106 daltons, respectively. The value for the 26 s RNA corresponds to roughly one turn of RF-I DNA. The RNA-synthesizing system contained no detectable RNase and the sizes of the RNA's synthesized were markedly different depending on the initial nucleotides. It is therefore suggested that RF-I DNA provided specific sites for the termination of RNA synthesis in addition to specific initiation sites. © 1969.