TEMPORAL AND SPATIAL REGULATION OF DEVELOPMENTALLY EXPRESSED GENES IN CAULOBACTER

Fundamental problems in developmental biology, such as the generation of asymmetry, differential transcription, and the execution of positional information, are all exhibited by a prokaryotic system, the Caulobacter cell cycle. Progeny cells resulting from each cell division have different developmental programs with respect to patterns of transcription and the initiation of DNA replication. The binary fission that yields dissimilar progeny results from asymmetry generated in the parent cell. An aspect of this fundamental developmental event is the temporally-controlled biogenesis of a polar flagellum. Several flagellar promoters require the histone-like protein, integration host factor (IHF) for transcription activation. IHF introduces bends in DNA resulting in the reorganization of the higher-order structure of the promoter region. These promoters appear to be transcribed from the chromosome in the swarmer pole of the predivisional cell. The newly replicated chromosomes in the predivisional cell differ in sedimentation coefficient and in the ability to initiate replication in the progeny cell. We hypothesize that the differential higher order structure of the two chromosomes contributes to both replication potential and transcription specificity.