In vivo transcription of Bacillus subtilis bacteriophage SPP1

The temporal program of SPP1 transcription was examined by hybridizing RNA extracted from infected B. subtilis cells, pulse-labelled at various times after infection, to restriction fragments of SPP1 DNA. RNA made early after infection hybridises to contiguous fragments in the left part of the SPP1 molecule, whereas hybridization to fragments in the right part of the chromosome is found late in infection. Viral gene transcription proceeds from right to left on the H-strand throughout the lytic cycle. At late times transcription occurs also from left to right using the L-strand as template. These assignments follow from the established 5'--3' polarity of the complementary (H- and L-) strains of SPP1 DNA and the determination of strand specificity in SPP1 transcription. Early and late transcriptions are also defined physiologically: protein synthesis and phage DNA replication must precede late transcription.