ANTISENSE RNA-REGULATED PROGRAMMED CELL-DEATH

Eubacterial plasmids and chromosomes encode multiple killer genes belo nging to the hok gene family. The plasmid-encoded killer genes mediate plasmid stabilization by killing plasmid-free cells. This review desc ribes the genetics, molecular biology, and evolution of the hok gene f amily. The complicated antisense RNA-regulated control-loop that regul ates posttranscriptional and postsegregational activation of killer mR NA translation in plasmid-free cells is described in detail. Nucleotid e covariations in the mRNAs reveal metastable stem-loop structures tha t are formed at the mRNA 5' ends in the nascent transcripts. The metas table structures prevent translation and antisense RNA binding during transcription. Coupled nucleotide covariations provide evidence for a phylogenetically conserved mRNA folding pathway that involves sequenti al dynamic RNA rearrangements. Our analyses have elucidated an intrica te mechanism by which translation of an antisense RNA-regulated mRNA c an be conditionally activated. The complex phylogenetic relationships of the plasmid-and chromosome-encoded systems are also presented and d iscussed.