ADP-ribosyltransferase that regulates transcription by ADP-ribosylation of host ribosomal protein S1. Additional identified targets include proteins involved in either translation or cellular metabolism such as elongation factor-Tu or trigger factor. Also reprograms the host's gene-expression system by RNAylating host ribosomal protein S1. ModB can attach NAD-capped RNAs to target proteins post-transcriptionally resulting in covalent RNA-protein conjugates