A transcriptional map of the bacteriophage SPO1 genome: III. A region of early and middle promoters (the gene 28 region)

Abstract

SPO1 gene 28, which codes for the positive regulator of middle transcription, gp28, has been mapped by in vitro DNA-directed protein synthesis to a segment located between 89.5 and 91.5 kbp from the left end of the genome. Gene 27 is also located in this interval. One early promoter has been mapped to this region of the genome (P E13 at 90.1 kbp) and early transcription of gene 28 could initiate there. Two other early promoters, P E14 and P E15, are located at 99.2 and 112.5 kbp from the left end. These three early promoters are significantly weaker in vitro than those early promoters which are located in the terminal repeat. The functions associated with P E14 and P E15 are unknown, but evidence is presented that P E15 is utilized in vivo. Thirteen middle promoters have also been mapped within the region of the genome extending from 85 to 113.5 kbp. The middle promoters are interspersed with the three early promoters and in some cases, yield overlapping early and middle transcription. Such overlapping early and middle transcription units apparently generate at least some em class SPO1 RNA in vivo.