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Impact of low temperature on genome-wide expression

In response to an abrupt drop in temperature, a change in gene expression has been postulated to allow for adaptation to the low-temperature environment (Sahara et al., 2002; Schade et al., 2004). This response is gene and time specific and involves the differential regulation of certain genes (Zhang et al., 2001, 2003; Sahara et al., 2002; Schade et al., 2004), presumably as a result of the altered physiological state of the cell caused by reduced membrane transport, accumulation of misfolded proteins, and reduced enzyme activity (Sahara et al., 2002; Schade et al., 2004). The early phase of the cold shock response involves adjustments to membrane fluidity and prevents destabilization of RNA secondary structures to allow efficient protein translation. The late phase involves the up-regulation of genes involved in the general stress response, including those encoding heat shock proteins and metabolic enzymes engaged in glycogen and trehalose metabolism (Sahara et al., 2002; Schade et al., 2004). Sahara et al. (2002) demonstrated that the genes involved in the general stress response are up-regulated following 4 hours of low-temperature exposure, whilst Schade et al. (2004) showed that they are still being up-regulated following 12 and/ or 60 hours of low-temperature exposure. The gene expression profile during growth at low temperatures (Homma et al., 2003) has been reported but this is to be differentiated from cold shock gene expression profiles since the former does not involve a sudden downshift in temperature.

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