A calcium-binding protein that may be required for the initiation of chromosome replication in Escherichia coli.

Starvation for isoleucine but not for other amino acids in an ilv- strain or the addition of valine in an ilv+ strain inhibits initiation of chromosome and minichromosome replication in stringent (Rel+) Escherichia coli, but it does not inhibit replication in relaxed (relA) mutants (Guzman et al, 1988). From these results, we concluded that, (1) oriC initiation of replication is inhibited by ppGpp, and (2) isoleucine is not needed for the protein synthesis required at initiation. These results led us to find an isoleucine-free protein whose de novo synthesis is the sole protein synthesis requirement for oriC initiation. We also present evidence that this protein may be a calcium-binding protein located at 73 min in the genetic map.