COMPOSITIONAL NUCLEOTIDE DISTRIBUTION AND THEORETICAL PREDICTION OF HOMOLOGY IN BACTERIAL DNA

A mathematical method is given for calculating the upper limit of possible DNA homology between any set of two bacteria; it depends on three parameters: the mean nucleotide composition, the molecular weight and the compositional nucleotide distribution of chromosomal DNA. The theoretical predictions are checked and confirmed by comparison with available experimental DNA hybridization data. The standard deviation of the compositional nucleotide distribution (expressed as molar per cent guanine + cytosine) of chromosomal DNA, was calculated for each of some 2500 different bacteria, belonging to 36 genera. The values range from 3 to about 5.5% GC, using an improved correction factor. When the mean nucleotide compositions of bacteria differ by at least 18 to 30% GC, there are almost no common nucleotide sequences and the organisms are evolutionarily far removed from each other and taxonomically unrelated. © 1969.