Abstract
The rate of total RNA synthesis, the extent of guanosine 3'(2')-diphosphate 5'-diphosphate (ppGpp) accumulation, and the pattern of protein synthesis were studied in light-deprived and heat-shocked Synechococcus sp. strain PCC 6301 cells. There was an inverse correlation between the rate of total RNA synthesis and the pool of ppGpp, except immediately after a temperature shift up, when a parallel increase in the rate of RNA synthesis and accumulation of ppGpp was observed. The inverse correlation between RNA synthesis and ppGpp accumulation was more pronounced when cells were grown in the dark. Heat shock treatment (47 degrees C) had an unexpected effect on ppGpp accumulation; there was a fairly stable level of ppGpp under heat shock conditions, which coincided with a stable steady-state rate of RNA synthesis even in the dark. We found that the pattern of dark-specific proteins was altered in response to heat shock. The transient synthesis of several dark-specific proteins was abolished by an elevated temperature (47 degrees C) in the dark; moreover, the main heat shock proteins were synthesized even in the dark. This phenomenon might be of aid in the study of cyanobacterial gene expression.
Highlights
Growing bacteria are strongly influenced by their nutritional, chemical, and physical environment, and they adjust their growth to alterations in these conditions in their habitat [19]
The heat shock phenomenon has recently been reported in Synechococcus sp. [6], and the response of the cells to elevated temperatures has been found to involve the reduction of growth rate and induction of a specific set of polypeptides, the so-called heat shock proteins
Experimental perturbation of growth alters the rate of stable RNA accumulation [9, 17]
Summary
Growing bacteria are strongly influenced by their nutritional, chemical, and physical environment, and they adjust their growth to alterations in these conditions in their habitat [19]. Since the reduction of growth during heat shock in Synechococcus and the nutritional or energy shift down in various cyanobacterial systems may have much in common with heterotrophic shift down systems, one would expect a role for ppGpp in the temperatureinduced regulation of stable RNA and protein synthesis in cyanobacteria. We describe the effects of heat shock on the synthesis of RNA and the accumulation of ppGpp upon transfer of Synechococcus cultures from light to darkness We relate these data to the pattern of proteins synthesized under heat shock [6] and in the dark (energy starvation [9]). Such studies are of interest in their own right, but from the viewpoint of light-dependent cyanobacterial gene expression as well
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