Secondary structure differences between normal and tumour DNA studied by UV-spectrophotometry.

Some differences between the structure of tumour and normal DNA were studied. An increase of the methylation degree of the tumour DNA was observed (by 42% as compared with normal DNA). Changes between normal and tumour DNA were found in the melting temperature (Tm), the melting interval (delta T) and the shape of the differential melting curves (DMC). In tumour DNA, two types of regions with changed thermostability were observed differing in length. The first type regions contain more than 20-30 pairs of nucleotides and manifest themselves on DNA DMCs as a low-temperature plateau. The other type, much shorter, cause a shift of DNA DMCs towards lower temperatures. The value obtained for the concentration of tumour DNA regions with changed thermostability per one pair of nucleotides is 4.4 x 10(-4). The in vivo influences of three alkylating preparations on the structure differences of both kinds of DNAs were studied. The preparations tested lowered the content of 5-mC in tumour DNA, altered the total concentration of DNA regions with changed thermostability, and effectively suppressed these regions containing 20-30 pairs of nucleotides. Also, a correlation was found between the effect of the preparations studied on tumour DNA and their ability to suppress the growth of Sarcoma 45.