Characterization of a Defective Mutant of the Dahlemense Strain of Tobacco Mosaic Virus

A mutant of tobacco mosaic virus has been isolated after treating the dahlemense strain with nitrous acid and called D 16y. Like dahlemense it produces necrotic lesions on java-type tobacco but induces a strong chlorosis on samsun tobacco, in which it spreads systemically. Yield of virus from infected plants is significantly lower than that of dahlemense and the virus particles are unstable in vitro, and probably also in vivo. It is serologically closely related to dahlemense, its coat protein is somewhat less electronegative in weakly alkaline medium and it is inactivated at elevated temperatures more easily than dahlemense. Its coat protein contains a histidine residue, that is not present in dahlemense. The poor biological activity and the instability of D 16y toward storage and high temperatures are properties that are common with many defective mutants. D 16y is possibly the first induced mutant of dahlemense and with its several altered characters is expected to be very useful for comparative studies on the structure and action of TMV.