| Abstract: | The photoaffinity label 8-azidoadenosine 5'-triphosphate (N3-ATP) was used to covalently modify the recA protein from Escherichia coli within its ATP-binding site. We have previously demonstrated that N3-ATP modification of recA protein is specific for the ATP-binding site and have isolated a unique tryptic peptide (T31), spanning residues 257-280, that contains the exclusive site of attachment of this ATP analog (Knight, K. L., and McEntee, K. (1985) J. Biol. Chem. 260, 867-872). We performed a secondary proteolytic digestion of the alpha-32P]N3-ATP-labeled T31 peptide using Staphylococcus aureus V8 protease and purified the resulting peptide fragments by high-pressure liquid chromatography (HPLC). Based on a comparison of the amino acid compositions of all purified fragments and sequence analysis of one labeled fragment we determined that Tyr-264 is the exclusive site of N3-ATP attachment in recA protein. Photoaffinity labeling of recA protein was also performed in the presence of single-stranded DNA. Following trypsin treatment and separation of peptides by HPLC we showed that tryptic peptide T31 contained the exclusive site of N3-ATP attachment. A secondary proteolytic digestion was performed on both alpha-32P]N3ATP-modified T31 and unmodified T31 using alpha-chymotrypsin. Comparison of the HPLC profiles and amino acid compositions of the resulting fragments was consistent with Tyr-264 as the exclusive site of N3-ATP attachment to recA protein. |
