A STATIONARY-PHASE-DEPENDENT VIABILITY BLOCK GOVERNED BY 2 DIFFERENT POLYPEPTIDES FROM THE RHSA GENETIC ELEMENT OF ESCHERICHIA-COLI K-12

Multicopy plasmids bearing a small internal portion of the RhsA geneti c element of Escherichia coli K-12 imparted a viability block on cultu res grown to stationary phase in broth. Inclusion of the last 25 codon s of the RhsA core open reading frame (called core-ORF) in the plasmid insert was crucial for eliciting this toxic effect. The toxic effect could be suppressed by including the adjacent Rhs component, dsORF-a1, an the multicopy plasmid. The toxic effect aas enhanced in RpoS(-) st rains.