The mutation of p53 gene was detected in Syrian hamster embryo（SHE） cells neoplastically initiated with a particles.The level of the p53 mRNA in transformant was obviously higher than that in non-irradiated counterpart

as measured by Northern blot analysis of total RNA.A pair of primers were designed based on p53 cDNA sequence to produce the whole length of coding sequence about 1.2 kilobase（Kb） by reverse transcription of mRNA followed by the polymerase chain reaction（RTPCR）

but the length of fragment amplified from transformant mRNA was about 0.3Kb

remarkably shorter than that from normal SHE cells.Imrnunohistochemical analysis of p53 protein showed that no heavy staining was found on slice of tumor derived from transformant inoculated in nude mice with hamster specific p53 monocloned antibody HD200.The results implied that p53 gene had been mutated by deletion

which might lead to loss of p53 protein expression but the increased expression of p53 remained in a particle-induced SHE transformant.