A 2.5-kb cDNA clone for human p53 tumor antigen has been isolated. This clone contains the entire coding region including 135 bp upstream of the first ATG. Comparison of the nucleotide sequence of human p53 and mouse p53 demonstrates that the first ATG in human p53 corresponds to the second ATG (codon No. 4) in mouse p53. The human p53 comprises 393 residues and is longer than the mouse p53 due to six additional codons present at the region corresponding to exon 4 of the mouse p53 gene. The DNA sequence homology between the coding regions of mouse and human p53 is 81% and the conservation of homology is not equally distributed along the molecule. When inserted into SV40-based expression vectors the human p53 cDNA successfully directs the production of a polypeptide with an apparent mol. wt. of 55 kd which can be precipitated by monoclonal antibodies to p53.
