The lacZ-hobH fusion clone, containing an Escherichia coli DNA segment loca
ted at 92 min on the chromosomal map, was screened as a producer of E. coli
oriC hemi-methylated binding activity. We have purified the protein encode
d by this locus to near homogeneity. The protein corresponds to the monomer
ic form of a non-specific acid phosphatase (NAP) whose gene has been design
ated aphA. oriC DNA footprinting experiments showed protection of hemi-meth
ylated probe by partially purified NAP, but not by purified preparations. Y
et, gel retardation experiments with an oriC oligonucleotide demonstrated D
NA binding activity of purified NAP in the presence of Mg2+. This experimen
t also showed an increased affinity of the protein for the hemi-methylated
probe compared with the fully or unmethylated form. Indirect immunofluoresc
ence microscopy revealed the existence of discrete NAP foci at mid-cell in
cells with two nucleoids but at cell poles in those with one nucleoid.