Heat-induced expression and chemically induced expression of the Escherichia coli stress protein HtpG are affected by the growth environment.

Differences in expression of the Escherichia coli stress protein HtpG were found following exposure of exponentially growing cells to heat or chemical shock when cells were grown under different environmental conditions. With an htpG::lacZ reporter system, htpG expression increased in cells grown in a complex medium (Luria-Bertani [LB] broth) following a temperature shock at 45 degrees C. In contrast, no HtpG overexpression was detected in cells grown in a glucose minimal medium, despite a decrease in the growth rate. Similarly, in pyruvate-grown cells there was no heat shock induction of HtpG expression, eliminating the possibility that repression of HtpG in glucose-grown E. coli was due to catabolite repression. When 5 mM phenol was used as a chemical stress agent for cells growing in LB broth, expression of HtpG increased. However, when LB-grown cells were subjected to stress with 10 mM phenol and when both 5 and 10 mM phenol were added to glucose-grown cultures, repression of htpG expression was observed. 2-Chlorophenol stress resulted in overexpression of HtpG when cells were grown in complex medium but repression of HtpG synthesis when cells were grown in glucose. No induction of htpG expression was seen with 2, 4-dichlorophenol in cells grown with either complex medium or glucose. The results suggest that, when a large pool of amino acids and proteins is available, as in complex medium, a much stronger stress response is observed. In contrast, when cells are grown in a simple glucose mineral medium, htpG expression either is unaffected or is even repressed by imposition of a stress condition. The results demonstrate the importance of considering differences in growth environment in order to better understand the nature of the response to an imposed stress condition.

Enhancement of a fra(16)(q22) with distamycin A: a family ascertained through an abnormal proposita.

A family in which a fragile site at 16q22 was segregating was ascertained through a newborn infant with multiple anomalies. The same fragile site was present in the phenotypically normal father and in a brother with cleft palate. The fra(16)(q22) was similar in appearance, and in response to culture conditions, to that reported by other investigators, including increased breakage in media supplemented with distamycin A. Sampling variation in the frequency of breakage over time may be considerable in some individuals. No pattern of anomalies was found to be associated with the fragile site. However, the reproductive history of the family we report (two livebirths with major congenital anomalies and one stillbirth) suggests caution in concluding fra(16)(q22) is not deleterious.