The natural 6 S RNA found in Q beta-infected cells is derived from host and phage RNA.

The RNA of Escherichia coli infected with RNA bacteriophage Q beta was isolated and screened for replicable short-chained RNA. In contrast to earlier assumptions we show that (i) short-chained replicable RNA is a very minor part of the RNA synthesized in the infection cycle, and (ii) that the replicable RNA isolated from infected cells is derived from cellular RNA, in particular 23 S rRNA and 10 Sa RNA, and from Q beta RNA itself. None of the many RNA species known from in vitro experiments was found. The RNA species isolated were all inefficient templates. No replicable RNA could be isolated from non-infected cells. Even in cells expressing high amounts of Q beta replicase very few RNA species could be isolated. RNA generated in vitro in template-free synthesis is therefore not derived from RNA species found in vivo, and replicable RNA found in vitro is generated by a mechanism fundamentally different from the one operating in vivo.