Biopolymers and cell. 1993. Volume 9. № 5. 54 - 61

MENDZHUL M. I., SYRCHIN S. A., AVERKIEV A. A., REBENTISH B. A.

The Way of Defence of Cyanophage LPP-3 DNA Against Restriction-Modification Systems in the Cells Cyanobacterium Plectonema boryanum

Summary

    HPLC method was used to study some peculiarities of cyanobacterium Plecloneina boryanum and cyanophage LPP-3 DNA composition. The elution profile analysis of the products of DNA acid hydrolysis enable to identify in DNA P. boryanum apart of canonical bases the presence of 4.5 % N-6-melhyladenine and 1.2 % 5-methyl-cytosine, DNA LPP-3 have 0,8 % 5-methyIcytosine and no N-6-methyladenine. The presence of 5-methylcytosine was detected only due to the application of the modified hydrolysis method HF. The restriction endonucleases-isoshisomers, DNA hydrolysis of which depend on presence of methylated bases in the recognition sites, were used to detect site-specific methylation. The comparison of the products of the DNA LPP-3 and P. boryanum fermentative hydrolysis by Mspl and Hpall; Sau3A, Mbol and Dpnl; Apyl and Mval restrictases enable to determined that DNA LPP-3 and P. boryanum has a high methylation degree of the inner cytosine in the CC(A/T)GG site and P. boryanum on the adenine in the GATC site; CCGG site wasn't methylated in both DNA. Proceeding from the data obtained a conclusion can be drown on the presence of dam- and dcml-like restriction—modification systems in P. boryanum. Defence of viral DNA against host R-M systems occur by cytosine methylation in sequence CmC(A/T)GG and counter-selection BamHI sites.