Transcriptional map of bacteriophage N4. Location and polarity of N4 RNAs

The strands of the four bacteriophage N4 DNA fragments derived by HhaI endonuclease digestion have been separated on agarose gels, and the eight fragments obtained have been related to the two complementary strands of N4 DNA. We have used the HpaI restriction endonuclease fragments (Zivin et al., 1980) and single-stranded fragments of HhaI-digested N4 DNA as probes to determine the temporal appearance, localization and polarity of N4 transcripts. These experiments have allowed us to localize on the N4 genome the two previously characterized classes (early and middle RNAs) of N4 rifampicin-resistant RNAs (Vander Laan et al., 1977) and to detect a new class of N4 RNAs, which are synthesized late in infection. The synthesis of late N4 RNAs is rifampicin sensitive and, as we show in this paper, requires the activity of the Escherichia coli RNA polymerase.