Endogenous ADP-ribosylation of two proteins with molecular weights of
30,000 (30K) and 80,000 (80K) was detected in cell extracts of Mycobac
terium smegmntis. Modification of these proteins was enzymatic. The AD
P-ribose bound to 30K was removed by HgCl2 but not by NH2OH, suggestin
g the modification of a cysteine residue. The ADP-ribose bound to 80K
was not removed by either HgCl2 or NH2OH, which is consistent with the
modification of an asparagine residue. ADP-ribosylation of 80K appear
ed to be reversible.