Factors Affecting the Selection of a Template for the Characterization of Multiple DNA-Dependent RIMA Polymerases of Mammalian Tissues

Abstract

The first step in the expression of genetic information in any cell is the production of an RNA transcript from the DNA by the DNA-dependent RNA polymerase. Factors that regulate the expression of certain genes or classes of genes might be expected to act by some direct effect on the transcription apparatus. The general picture that has emerged from a study of gene-expression control in prokaryotes tends to support this thesis. Our understanding of the phenomenon of “polymerase-mediated control” has developed from investigations of bacteriophage infection of Escherichia coli. It is now generally accepted that host E. coli RNA polymerase transcribes at least a part of the phage genome (the “early” regions), whereas a modified host RNA polymerase (in the case of T4) or even a new phage-specified polymerase (as in the case of T7) transcribes the “late” regions (1,2). These observations suggest that the host E. coli RNA polymerase, the modified T4 polymerase, and the new phage-specified polymerase recognize different nucleotide sequences and thus bind to and transcribe from different initial binding sites (promoter sites) on phage DNA. Thus at least one “positive” control mechanism resides in the ability of different polymerase species to recognize different promoter sites.