Figure 23-3: The bacteriophage SPP1 mature chromosome. The two main bars denote the mature phage sequence (1 to ~45.9 kb). The upper line of the bar represents the H (heavy) strand and the lower line the L (light) strand. The representation of the 16 EcoRI DNA fragments, the dispensable, early and late gene regions, early and late promoters; oriL and oriR, are according to figure 23-2. Fragment EcoRI-13t has one end generated by EcoRI digestion and the other by cleavage at the pac site by the terminase enzyme. The pac region is located within EcoRI DNA fragment 1 (uncleaved: pacLCR, solid black box indicated by vertical arrow). The cleaved pac site (pacCR, solid black oval, indicated by a vertical arrow) defines the first nucleotide of the SPP1 sequence. To present the full EcoRI DNA fragment 1, the first 718 bp (defining the EcoRI-13t fragment) are shown again in the upper main bar after position 44007 (broken line). Therefore, gene 1 is also presented twice. Due to imprecision of the headful cut mechanism the end of the mature SPP1 chromosome (~45.9 kb) is not precisely defined. The numbered hatched boxes denote phage-encoded products that have been genetically or biochemically characterized, whereas the empty ones indicate those of unknown function (3).