FIG. 2.

Construction of nox null mutants. Insertional inactivation of nox in two unrelated strains of S. pyogenes was accomplished by first amplifying a region internal to the nox coding region (noxtrunc) and then inserting the fragment into integrational vector pCIV2. The resulting element, pNOX1, contains a kanamycin resistance determinant (striped bar) and the noxtrunc region (empty bar) of JRS4. Recombination between homologous regions of pNOX1 and the S. pyogenes JRS4 and HSC12 chromosomes (indicated by the large X between the plasmid and chromosomal restriction maps) generated JNOX1 and HNOX1, respectively, which have a chromosomal structure that contains two truncated and inactive versions of nox (indicated by the zigzag line). E, EcoRI; H, HindIII; N, NcoI; Nd, NdeI; P, PstI; Sc, ScaI; Sm, SmaI; ORI, origin of replication.