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An Analysis of Restriction Endonuclease Sites in Cyanophages Infecting the Heterocystous Cyanobacteria Anabaena and Nostoc

I. Bancroft

Department of Biological Sciences, University of Lancaster, Lancaster LA1 4YQ, U.K.

An analysis of restriction endonuclease cleavage of DNA isolated from cyanophages that infect Anabaena and Nostoc species of cyanobacteria has provided evidence for counter-selection of restriction endonuclease sites. These include sites containing subsequences which are methylated by host (Anabaena PCC 7120) methylase(s) akin to the dam and dcm enzymes of Escherichia coli. Other sites which are counter-selected have no common sequence structure. The latter include those of the endogenous restriction endonucleases of the host, but other absent sequences are not attributable to isoschizomers of any known Anabaena or Nostoc restriction endonuclease. The cyanophages differ in their tolerance to DNA methylation. Isolates A-4L, AN-13 and AN-23 do not tolerate adenosine methylation in the GATC sequence whereas two cyanophages, A-1L and AN-10 (which are related) do tolerate dam-like methylation of this sequence. In addition, A-1L allows cytosine methylation at GGCC sequences, but AN-10 has counter-selected these sequences and the remaining sites are not methylated. Analysis of native and cloned A-4L DNA suggests that counter-selection has occurred against all sequences which would be methylated by the host at either adenosine or cytosine nucleotides.

Keywords: cyanophages, heterocystous cyanobacteria, DNA methylation

Present address: MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824, U.S.A.

Received 12 May 1987; accepted 18 December 1987.

This article has been cited by other articles:

				A. V. Matveyev, K. T. Young, A. Meng, and J. Elhai DNA methyltransferases of the cyanobacterium Anabaena PCC 7120 Nucleic Acids Res., April 1, 2001; 29(7): 1491 - 1506. [Abstract] [Full Text] [PDF]