The relation between the processes of replication and transcription has been actively studied over several decades, but detailed mechanisms for their interaction have not been established reliably. Among the initiating transcription promoters of bacteria and bacteriophages, there are both promoters having an additional function of the secondary origin of replication (OR) and promoters not participating in this process. In this paper, we describe the stability of DNA by Stress-Induced Duplex Destabilization (SIDD) profiles for a complete set of promoters and the primary OR of the bacteriophage T7 genome. It has been shown that, among the native T7 promoters, only those that have an additional function of secondary OR are characterized by high destabilization. These include the phiOL and phiOR promoters adjoining the 5' and 3' terminal repeats of bacteriophage T7, and of six other T7 group phages. In each case, these two promoters are located in the regions of DNA with high destabilization of the duplex. Additionally, the genomes of seven representatives of the T7 group without annotated phiOL and phiOR have been considered. For three of them, high peaks of SIDD profiles have been found near the ends of the genomic DNA that may be due to the presence of similar phiOL and phiOR promoters. Probably, such promoters can be found in the genomes of other bacteriophages. Thus, for the promoters of bacteriophages, we have a confirmation of the relationship of SIDD as a DNA duplex parameter and the DNA replication initiation on promoters, serving as secondary OR.