The T7 RNA polymerase-dependent transcription was studied as a function of nucleotide sequence structures positioned upstream of the T7 promoter. Model double-stranded DNA templates were constructed for this purpose. They contained a target sequence of 485 base pairs (cDNA fragment of Venesuelian encephalomyelitis equine virus genome), T7 promoter consensus and different extra base sequences upstream of the T7 promoter. The level of the target sequence transcription was clearly determined by the extra base sequence. The presence of one extra base pair G.C ensured the most pronounced effect, transcription was increased one order of magnitude in comparison with template which has only a canonical T7 promoter sequence at the 5'-end.

The BstF5I restriction-modification system from Bacillus stearothermophilus F5 includes four site-specific DNA methyltransferases, thus differing from all known restriction-modification systems. Here we demonstrated for the first time that one bacterial cell can possess two pairs of methylases with identical substrate specificities (methylases BstF5I-1 and BstF5I-3 recognize GGATG, whereas methylases BstF5I-2 and BstF5I-4 recognize CATCC) that modify adenine residues on both DNA strands. Different chromatographic methods provide homogenous preparations of methylases BstF5I-2 and BstF5I-4. We estimated the principal kinetic parameters of the reaction of transfer of methyl group from the donor S-adenosyl-L-methionine to the recognition site 5;-CATCC-3; catalyzed by BstF5I-2 and BstF5I-4 DNA [N6-adenine]-methyltransferases from the BstF5I restriction-modification system.

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