A mutation that converts serine super(340) of the HsdS sub(K) polypeptide to phenylalanine and its effects on restriction and modification in Escherichia coli) K-12

A hybrid hsdS gene, encoding the HsdS sub(t) sub(s) super(+) super(d) polypeptide, was constructed by joining the proximal region of the wild-type hsdS sequence with the distal region of the hsdS sub(t) sub(s) super(+) super(d) sequence, at the hsdS BglII site. The hybrid hsdS-S sub(t) sub(s) super(+) super(d) gene exerts a trans-dominant effect on restriction and modification, which points to the location of the temperature-sensitive trans-dominant (+d) mutation in the gene hsdS sub(t) sub(s) super(+) super(d) distal region. Sequencing of the region downstream from the HindIII target in the Escherichia coli) K-12 hsdS sub(t) sub(s) super(+) super(d) mutant was carried out.