The distribution of the electrostatic potential of T7 bacteriophage genome has been calculated. Promoter sites were localized in the electrostatic profile of T7-DNA. The electrostatic patterns of sigma70-specific promoters interacting with Escherichia coli RNA-polymerase were analyzed and compared with their functional behavior. Some specific electrostatic motifs were found in the upstream region of the promoters that may be involved in the differential recognition of promoter DNA by RNA-polymerase.