De novo methylation of selective CpG dinucleotide clusters in transformed cells mediated by an activated N-ras.

We have explored a possible role of an activated N-ras oncogene in aberrant methylation of CpG clusters in DNAs of transformed cells. Using three lines of hamster cells transformed by Rous sarcoma virus (RSV) and the method of detection of CpG islands as clustered sites for methylation-sensitive restriction enzymes we have demonstrated that in each cell line the transcribed RSV proviruses are integrated in the vicinity of sequence containing the cluster of unmethylated CpG dinucleotides. Two out of three examined CpG clusters had hypermethylation patterns in N-ras-neo- but not in neo-transfected variants of the cell lines. De novo methylation of CpG dinucleotides correlated with transcriptional inactivation of adjacent RSV proviruses that was related neither to the lack of transcriptional factors binding RSV long terminal repeat (LTR) nor to the transcriptional incompetence of the LTR, as measured by reporter gene assays with the LTR cloned from DNA of these cells. These data suggest that activation of N-ras signal transduction pathway in transformed cells may be relevant to long-term inactivation of selective genes by hypermethylation of their CpG islands.

[Medium proteins as a factor of regulation of the synthesis of secreted proteinases]. / Belki sredy kak faktory reguliatsii sinteza sekretiruemoi proteinazy.

It was shown that medium proteins possess a double regulatory effect on the synthesis of proteinase secreted by Aspergillus awamori 78-2. These proteins are nitrous nutrition that provides for the utilization of the proteolysis products in the course of their gradual formation, which excludes their inhibiting action on the enzyme synthesis. On the other hand, medium proteins possess the ability to induce secreted proteinase synthesis. It is assumed that the concept "enzyme synthesis inducer" can be applied to any one of its substrates, which stimulates protein synthesis at any level and via any mechanism.