A brief chronology of our investigations

As an enzyme, I chose acid DNase (which we had isolated for the first lime), because preliminary experiments indicated that this enzyme led to the degradation of DNA into very large fragments of about 1 kb (Bcmardi el al., I960). The study of this and other DNases provided the first demonstration that these enzymes recognize short DNA sequences, contrary to the prevailing view (Laskowski. 1971, 1982) that they lacked specificity. It also indicated that acid DNase could cut both strands of native DNA at the same 

These nucleotides had compositions that were characteristic of the DNA under study (and of the DNase used). Since the pereentages of the termini formed by DNases from bacterial DNAs were linearly related to their GC levels (Fig. 1.3A), a useful way to show the results from the DNAs under examination was to plot difference histograms like those of Fig. 1.3B. This approach extended the nearest neighbour analysis of dinucleotide frequencies (Josse et al., 1961) to a frequency approach involving the sequences, at least four 

As a fractionation method, I developed chromatography of nucleic acids on hydroxyapatite, a calcium phosphate which had been used by Tiselius et al. (1956) for the fractionation of proteins. Previous observations (Bernardi and Cook, 1960a,b,c) that hydroxyapatite was particularly good as a chromatographic substrate for fractionating of phospholipoproteins characterized by different phosphorylation levels convinced me to try it on DNA. The main discovery was that hydroxyapatite could fractionate single- from double-stranded DNA (Fig. 1.4 left panel), the former being eluted by a lower phosphate 

In 1966,1 also started a long-term project on the molecular genetics of yeast mitochondria. This model system provided important results as far as both the organization and the evolution of eukaryotic genomes are concerned. These findings will be briefly presented and discussed in Part 2 of this book. In the 1960 s we also performed a series of investigations on the physical chemistry of DNA (see, for instance, Froelich et al., 1963 Freund and Bernardi, 1963) and on transforming DNA from Haemophilus influenzae (Chevallier and Bernardi, 1965, 1968 Bernardi and Bach, 1968 Kopecka et al., 1973). 

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