A 53-kilodalton protein common to chemically and virally transformed cells shows extensive sequence similarities between species.

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Abstract
A heat-stable DNA-binding protein with subunits of .apprx. 53 kilodaltons (kD) was purified from 2 virally transformed human cell lines (Epstein-Barr virus-positive Raji and Namalwa) and 2 mouse tumor cell lines (methylcholanthrene-induced Meth A sarcoma and TA3 mammary carcinoma). All four 53-kD proteins showed closely related total amino acid compositions, similar peptide maps and identical NH2-terminal amino acid sequences for 20 residues. These 53-kD proteins are therefore evolutionarily highly conserved, independent of whether they originate from virally or chemically transformed cells. The NH2-terminal sequence and the protein chain as a whole are not hydrophobic; however, some unexpected residue distributions were observed. Comparisons with other proteins reveal no clear sequence similarity with known tumor antigen structures, homologous Ig or other proteins of known sequence. Epstein-Barr virus-determined nuclear antigen also appears to have a different NH2-terminal sequence. Thus the 53-kD proteins represent a unique protein type with little species variation; these proteins may perform an important common function in different transformation systems.