Escherichia coli genome is composed of two distinct types of nucleotide sequences

We calculated correlations of the nucleotide distributions along the E. col i genome. Subsequent cluster analysis of the correlation distributions show ed that the genome was composed of two qualitatively different types of nuc leotide sequences. The first type exhibited strong correlations of the geno mic distributions of A with T and G with C, and high anticorrelations of A with C and G with T. In contrast, the second type was characterized by weak or negligible correlations typical of randomized sequences, Both types of sequences were almost equally abundant in the E, coli genome and their leng th varied from several hundred nucleotides to about 70 kilobases, They were not disjunct with respect to their (G + C) content but the high correlatio ns and anticorrelations were rather characteristic for (A + T)-rich genomic segments, We offer possible explanations of the mosaic structure of the E, coli genome. (C) 2000 Academic Press.