ADP-ribosyltransferase that efficiently ADP-ribosylates both alpha subunits of host RNA polymerase RPOA (PubMed:15489438, PubMed:10634320). The ModA-induced ADP-ribosylation of RPOA alpha subunits inhibits transcription from viral early promoters (PubMed:7031602). L-arginyl-[protein] + NAD(+) = H(+) + N(omega)-(ADP-D-ribosyl)-L-arginyl-[protein] + nicotinamide This protein is injected from the virion into the bacterial cell. Belongs to the Tevenvirinae NAD--protein ADP-ribosyltransferase modA family.