Synthesis of Bacterial Flagella: Chromosomal Synchrony and Flagella Synthesis

Synchronous cultures of Bacillus subtilis 168 M were obtained from light-density spores germinated at 46 C and grown at 37 C. This procedure synchronizes both cell division and chromosome replication. The chromosome synchrony was demonstrated by using transformation to measure changes in marker frequency during the cell cycle. The synthesis of two enzymes and of bacterial flagellar protein was also followed. All of the proteins were found to be synthesized continuously with an abrupt doubling in the rate of synthesis at a specific time in the cell cycle. The time at which the doubling occurred for each enzyme corresponded to the time at which the structural gene for the enzyme was replicated. The doubling of the rate of flagella synthesis corresponded to the time of replication of the hisA1 gene. We conclude that the genetic locus for the factors involved in the rate-limiting steps in flagella synthesis are located on the genetic map near the hisA1 locus.     

The Pragmatic Approach to Masking

This paper advocates the use of a pragmatic approach to the problem of masking in real-life situations involving an abrupt change in the timing of sleep, i.e. shiftwork and “jet-lag” situations. Although “pure” chronobiological research has pointed to the importance of taking masking effects into account, the techniques that it has provided for doing so are extremely difficult to apply in real-life situations. The approach advocated here is based on Wever's pioneering work, and involves estimating the normative endogenous and exogenous components of the circadian rhythm in body temperature. These estimates are then used to: (a) simulate the results of shiftwork studies; and (b) to “remove” the exogenous component in “jet-lag” studies to allow analysis of the estimated endogenous component. The simulated curves obtained cross-correlated extremely highly with published night-shift temperature curves, while the “removal” of the exogenous component resulted in very similar findings to those obtained in temporal isolation studies. It is concluded that this pragmatic approach to masking may prove extremely useful in interpreting the results of field studies of shiftwork and “jet-lag”.