HUMAN P53 WITH A MUTATION IN CODONE-273 F ACILITATES THE AMPLIFICATION OF THE GENE DHFR IN RAT-1 AND LIM1215 CELLS

The effect of the expression of the exogenous human mutant p53 (Arg -- > His in codone 273) on the amplification rate of the gene dhfr in per missive Rat-1 and LIM1215 cells was studied. It was shown that injecti on of a retroviral construction with p53His273 resulted in the accumul ation of methotrexate-resistant variants with an increased number of d hfr copies in populations of recipient cells. Luria-Delbruck fluctuati on analysis revealed a four- to six-fold increase in the rate of appea rance of new methotrexate-resistant cells. Chromosomal analysis demons trated an extrachromosomal location of amplified DNA in cells containi ng p53His273, as was the case for control sublines. The data obtained indicate that modifications of p53 may induce gene amplification not o nly via removing the proliferation block of cells with amplified genes in selective medium, but also via some other mechanisms, that seem to increase the chromosomal recombination rate.