Symmetrical Transcription in Animal Cells and Viruses

Abstract

I would like to discuss the first step of genetic transfer, that from DNA to RNA, namely the transcription process. It is assumed that there is a selectivity in transcription; thus, not all the genetic information of the DNA is transcribed to RNA; there is transcription of only portions of certain DNA templates and non-transcription of others. In other words, in vivo transcription proceeds from defined initiation points to defined stopping points. There is another type of selectivity in the transcription process: It has been generally accepted that transcription is asymmetric, in the sense that only one strand of a given gene is transcribed. The idea of asymmetric transcription is based on the assumption that if each of the two DNA strands of a given gene serves as an RNA template, each gene would produce two RNA products with complementary sequences, which should code for two different proteins. Since, from genetic evidence we know that each gene controls only one protein, we must assume that either only one of the two possible RNA strands is made, or if both are synthesized, for some specific reason, only one is functional. Using bacteriophages as model systems, it appeared that the former possibility is correct and since then the dogma is that in vivo transcription is asymmetric.