Enzymatic Synthesis of Ribonucleic Acid. Iv. the Deoxyribonucleic Acid-directed Synthesis of Complementary Cytoplasmic Ribonucleic Acid Components.

The ribonucleic acid product formed by ribonucleic acid polymerase resembles its deoxyribonucleic acid template in base composition and in base sequence (l-6). The reaction in vitro results in the synthesis of RNA chains which are complementary to both DNA strands (6). Evidence for this originates from the formation of highly ordered RNA structures when the RNA polymerase product is annealed with itself (7), and from base composition analysis of the polymerase product when primed by single or double stranded +X174 DNA (8, 9). Self-annealed synthetic complementary ribonucleic acid exhibits properties very similar to helical DNA (7). Although RNA polymerase catalyzes the synthesis of two complementary ribopolymers in vitro, studies with bacteriophage systems have led to the conclusion that informational RNA results from the transcription of only one DNA strand in wivo (10-12). It is not yet certain whether the bacteriophage systems represent a general transcription mechanism or a specialized case. Recently, Hayashi, Hayashi, and Spiegelman (13) reported that when a “replicating form” of @X174 DNA is used in the RNA polymerase reaction in vitro, only one DNA strand is copied. Observations by other investigators have led to the belief that the synthesis of most, if not all, cytoplasmic RNA is under the direction of DNA. Enucleated cells show a rapid drop in the content of their cellular RNA (14). Actinomycin D, an inhibitor of RNA polymerase, prevents the synthesis of cytoplasmic RNA when given to whole cells (15). Other evidence in support of this concept is the demonstration of specific RNA-DNA hybrid formation between microbial cytoplasmic ribonucleic acids and homologous DNA (16-18). Hybrid formation of this type implies the presence of nucleotide sequences in cytoplasmic RNA which are complementary to base sequences in DNA. Therefore, DNA directs not only the synthesis of template RNA for protein synthesis, but ribosomal and transfer ribonucleic acids as well. The high degree of self-complementarity among the RNA chains formed by RNA polymerase suggested the possibility that the self-complementary ribonucleic acid product might contain one strand which was identical in base sequence with ribosomal and transfer RNA, and the other strand complementary to