ABSTRACT

A Point Mutation in the p53 Tumor Suppresor

Gene in DAOY Cell Line

By

Luis Lopez

     Mutations in the p53 tumor suppressor gene are found 

frequently in human mammary, colon, and bladder carcinomas.  In 

this study, a brain tumor cell line, DAOY, was evaluated for 

the presence of similar mutations.  Previous analysis of the 

DAOY genomic DNA has revealed that the human p53 tumor 

suppressor gene has lost its heterozygosity and that the 

remaining p53 allele produced p53 mRNA of normal size (Raffel, 

1990).  To test the possibility that the remaining p53 allele 

was the target of mutation, a sequence analysis of the 

evolutionarily highly conserved region of p53 cDNA was carried 

out and showed that a point mutation of guanine to thymine 

transition occurs at codon 242.  When normal, base 725 is part 

of a cysteine codon (TG725C); when mutated, it becomes a 

phenylalanine codon (TT725C).  These results have led to a 

general model of tumorigenesis requiring loss of both alleles 

at a tumor suppressor locus.  This study has also started to 

test for the effect of expression when a wt-p53 is transfected 

into DAOY cell line.  Among 9 G418-resistant clones screened, 

3 showed the right molecular size of cDNA p53 when analyzed by 

Southern Blotting techniques.