Fourier spectra of E. coli promoter DNA sequences have been obtained. The periodical structure of individual promoter sequences is characterized. E. coli promoter sequences are classified according to their Fourier spectra using three feature sets: 1--the number of peaks in Fourier spectra; 2--values of power spectra for promoter primary structures and their similarity with physical periodicities in the backbone of polynucleotide; 3--the presence of blocks made of equal nucleotides. The comparison of Fourier spectra of promoter sequences and corresponding genes is provided. The conclusion that different ways of stabilization of promoter secondary structure in the case of different primary structure periodicities is drawn. The intermittence of AT- and GC-blocks, and variety of Fourier spectra mean DNA hydrate shell in DNA promoters is non-contiguous and non-stable at junction points. Characteristic features of prokaryotic promoters Fourier spectra differ from human promoters.