Increased expression of a hemimethylated oriC binding protein, SeqA, in anaphA mutant

In Escherichia coli, the origin of DNA replication, oriC, becomes transient ly hemimethylated at the GATC sequences immediately after initiation of rep lication and this hemimethylated state is prolonged because of its sequestr ation by a fraction of outer membrane. This sequestration is dependent on a hemimethylated oriC binding protein such as SeqA. We previously isolated a clone of phage lambda gt11 called hobH, producing a LacZ fusion protein wh ich recognizes hemimethylated oriC DNA. Very recently, Thaller et al. (FEMS Microbiol. Lett. 146 (1997) 191-198) found that the same DNA segment encod es a non-specific acid phosphatase, and named the gene aphA. We show here t hat the interruption of the aphA reading frame by kanamycin resistance gene insertion, abolishes acid phosphatase (NAP) activity. Interestingly, in th e membrane of the null mutant, the amount of SeqA protein is about six time s higher than that in the parental strain, suggesting the existence of a re gulatory mechanism between SeqA and NAP expression. (C) Societe francaise d e biochimie et biologie moleculaire / Elsevier, Paris.