Host specificity of DNA in Haemophilus influenzae: the in vivo action of the restriction endonucleases on phage and bacterial DNA.

In Haemophilus influenzae strains only the type 1 of the restriction endonucleases have an in vivo effect on phage and bacterial transforming DNA. The type 2 of restriction endonucleases which act very efficiently in vitro are completely inactive in vivo. The reasons for this inactivity is unknown.