[p53 with a mutation in codon 273 increases the probability of amplifying the dhfr gene in Rat-1 and LIM1215 cells].

The effect of the expression of the exogenous human mutant p53 (Arg-->His in codon 273) on the amplification rate of the gene dhfr in permissive Rat-1 and LIM1215 cells was studied. It was shown that injection of a retroviral construction with p53His273 resulted in the accumulation of methotrexate-resistant variants with an increased number of dhfr copies in populations of recipient cells. Luria-Delbruck fluctuation analysis revealed a four- to six-fold increase in the rate of appearance of new methotrexate-resistant cells. Chromosomal analysis demonstrated an extrachromosomal location of amplified DNA in cells containing p53His273, as was the case for control sublines. The data obtained indicate that modifications of p53 may induce gene amplification not only 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.