Host specificity of DNA in haemophilus influenzae: The physiological and genetical bases of instability of restriction and modification of DNA in strain Rd.

Further investigations of the instability of restriction and modification properties of H. influenzae Rd strain were carried out. It has been shown that the instable properties of hsd Hind1 system are maintained even after transfer of this system to another H. influenzae strain. The expression of hsd Hind1 system is very sensitive to various physiological changes which do not influence the other hsd systems present in the same Rd strain. The instability of hsd Hind1 system is postulated to be connected with some regulator gene(s).