Viral Harvey ras p21 expressed in Escherichia coli purifies as a binary one-to-one complex with GDP

The ras oncogene of Harvey murine sarcoma virus encodes a 21,000-dalton protein, p21, which mediates transformation. Viral Harvey ras p21, cloned into Escherichia coli HB101 lambda/pRAS1, has been purified to homogeneity by a three-step procedure. The purified E. coli p21 can be bound by a monoclonal antibody to viral Harvey ras p21 and has an amino acid composition consistent with that predicted from its DNA sequence. Purified E. coli p21 has been shown by HPLC analysis on an ion-exchange column to contain near stoichiometric amounts of GDP. This noncovalently associated GDP is seen in the UV absorption spectrum of the purified protein. The noncovalently associated GDP acts as a competitive inhibitor of the interaction of added guanine nucleotides with p21.