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Methylated Bases in the Single-stranded DNA Phages

Aharon Razin


The widespread occurrence of methylated bases in the DNA of living organisms and the species-specific pattern of DNA methylation (Hall 1971) strongly suggest that these methyl groups play an important biological role. At the present time, however, few biological processes can be correlated with methylated bases in DNA.

Most of the methylated bases in the bacterial chromosome are not related to the modification activity in these cells, since bacteria that are devoid of a restriction-modification (R-M) system still methylate their own DNA. The function of these methyl groups, as well as of those found in eukaryotic cell DNA, is obscure.

The single-stranded DNA bacteriophages, which possess a few methyl groups per genome, are ideal tools for studying the role of DNA methylation. Thus, the filamentous bacteriophages f1, fd, and M13 have been investigated with respect to the function of the methylated bases in the R-M phenomena (Arber 1968). The isometric phage ϕX174, which is not subject to R-M and is propagated in Escherichia coli C, a strain devoid of any known R-M system, was chosen to study the role of methylated bases not related to R-M. A single methyl group has been found in the ϕX genome and it has been suggested that this group is essential in the final stages of phage maturation (Razin et al. 1975).

ϕX is not restricted by the EcoK or EcoB R-M systems,1 whereas the filamentous phages fd, f1, and M13 are restricted and undergo host-controlled modification in...

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