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The critical moment of regulation when transition of the cell from the G1 to the S phase takes which is decisive for its division is the so-called R-point (restriction point). The disorder of molecular mechanisms controlling the passage of the cell through this site is an associated manifestation of most tumourous processes. A considerable part of this mechanism is the RB protein, binding transcription factors needed for the activation of genes effective in the S phase. Its binding capacity depends on the extent of phosphorylation and on the activity of the appropriate kinases and their inhibitors.

In 26 top sportsmen (volleyball players, rower) aged 15-18 years the serum magnesium level and urinary Mg excretion before and after oral administration of 5 g Mg lactate was assessed (oral magnesium load test). In 11 sportsmen (42.3%) a low percentage of excretion of administered Mg was found, suggesting magnesium deficiency, irrespective of the basal serum Mg levels. After subsequent 10-day Mg supplementation 6 volleyball players responded by a markedly lower retention after an identical Mg load, again without marked changes of the serum Mg level. The authors consider the magnesium load test a more sensitive indicator of latent Mg deficiency than the serum Mg level which is maintained at a relatively stable level and declines only in severe deficiency. The test assumes normal renal function and intestinal absorption.

The results of the present study of the p53 antioncogene in a broad panel of human cell lines (n = 32) and biopsy specimens (n = 435) from both normal and tumour tissues can be summarized as follows: 1. Cells in primary cultures from normal tissues express very low levels of the p53 protein while strong nuclear accumulation of p53 can be seen in all SV 40 transformed human cell lines and the vast majority of tumour--derived cell lines studied. 2. Similarly, in human tissues strong nuclear p53 expression is found in high proportion of malignancies of various histogenesis, in contrast to benign lesions, nonmalignant tissues surrounding malignant tumours and normal tissues in which the p53 protein levels remain below the limits detectable by common immunohistochemical methods. 3. Sequence analysis of p53 mRNA amplified by polymerase chain reaction (PCR) revealed point mutations in the central region of the p53 gene in several cancer cell lines. Furthermore, very good correlation was found between the presence of such mutations and accumulation of the mutated p53 protein. This study confirms and extends our current view of p53 as the gene most frequently altered in human cancer and suggests that simple immunohistochemical methods can be used to screen for aberrations of this antioncogene.

The expression of intermediate filaments during tissue differentiation, in mature tissues and in their neoplastic derivatives (lungs, thyroid gland, kidney, uterus, CNS) was investigated by means of monoclonal antibodies prepared in our departments (Institute of Molecular Genetics, Czechoslovak Academy of Sciences, Prague and in the Department of Immunology and Molecular Biology, Brno). The conclusions of these investigations provide evidence of the restricted specificity of detection of intermediate filaments in relation to germ layers and mesenchymal vs. epithelial set-up of tissues and the need of knowledge of the differential programme of a given tissue for the interpretation of the presence of intermediate filaments in tumours which develop from it.