An inhibitor of RNA polymerase II is described, wherein said inhibitor is selected a moiety which targets a protein selected from cyclin kinase 12 (CDK12) or its recruiting protein PAF1C. Particular examples of such inhibitors are polypeptides expressed by a gene selected from lldD, lldR, nlpD or rfaH of a bacterial species, such as a commensal bacteria or asymptomatic carrier, or a variant of said protein. Inhibitors may be based upon bacterial Sigma S or NplD proteins. These inhibitors are useful in therapies, to suppress protein expression. Thus they may be used as immunosuppressants, anti-inflammatory or anti-infection agents.
