On the inhibition of phage production by 2-thiouracil and 8-azaguanine in an induced lysogenic Bacillus megaterium

Abstract

Thiouracil exerts an inhibitory influence on induced lysogenic Bacterium megaterium that is much more extensive on phage protein and phage DNA synthesis than on bacterial protein and DNA synthesis. The number of infectious phage particles produced decreases more than does the amount of phage protein. The action of thiouracil is reversible by uracil, but not by thymine nor thymidine. Ultraviolet irradiation suppresses the inhibitory effect of thiouracil unless the cells have been in contact with the latter for 30–60 min preceding irradiation. Thiouracil incorporation into RNA is also suppressed by ultraviolet irradiation. Nevertheless, a considerable amount is incorporated if the thiouracil is added 30 min before irradiation. The parallelism which seems to exist between incorporation of thiouracil into RNA and its inhibitory action on phage protein synthesis is consistent with the hypothesis that a particular fraction of RNA participates in the synthesis of phage constituents and that thiouracil influences phage synthesis by being incorporated into this fraction. Though the phenomenon is not so readily observed, azaguanine also seems to exert a selective inhibitory action on the synthesis of phage protein and phage DNA in induced lysogenic Bacterium megaterium. This analogue is also incorporated into RNA and it is assumed that its mode of action is similar to that of thiouracil.