Reference no: EM13163070

A single-stranded RNA phage replicates in E. coli with no DNA intermediates. The following experiments were performed to clarify the phage's mode of replica tion. A. When phage RNA was extracted from infected cells and centrifuged in a sucrose gradient, three fractions were observed. Fraction 1had molecules of the same size, which were shown to be single-stranded. Fraction 2 had molecules of the same size, which were shown to be double-stranded. Fraction 3 had molecules of various size, varying from 1 to 1.5 times the molecular weight of those in Fraction 2. B. A phage-infected E. coli culture was exposed to a short pulse of radioactivelylabeled uridine. When the phage RNA was extracted and centrifuged by the procedure in experiment A, most of the radioactivity was found to reside in Fraction 3. C. Fraction 3 from experiment B was removed and subjected to pancreatic ribonuclease. About half of the radioactivity was released in acid-soluble form. D. Fraction 3 from experiment B was removed and subjected to pancreatic ribonuclease, then centrifuged as in experiment A; there was only a single band, at the same position as Fraction 2 in experiment A. Show, by means of words and drawings, how this RNA phase replicates itself.