N4 virion DNA dependent-RNA polymerase: initiation sequences utilized by the enzyme on heterologous templates.

Bacteriophage N4 virion-encapsulated RNA polymerase, the enzyme responsible for transcription of the phage early RNAs, is unable to use duplex linear DNA as a template. In contrast to other RNA polymerases, the enzyme transcribes denatured N4 DNA with in vivo specificity. The promoter sequences for three sites of transcription initiation on the N4 genome have been determined and found to contain conserved sequences and two sets of inverted repeats. In order to define the minimal sequence requirements for N4 virion RNA polymerase activity, we have screened several heterologous DNAs, amounting to 64,328 bases, for their ability to support transcription. Several sequences allowing specific initiation were found. Their location, properties and the relation to N4 virion RNA polymerase promoters are discussed.