Int. J. Environ. Res. Public Health 2010, 7 948 This proposed mechanism perfectly explains several previously inexplicable data, such as alteration of circadian rhythms in laboratory animals and humans during extremely low frequency EM radiation exposure [61,62], and the pronounced increase in transcription in cells exposed to ELF EMF [63]. The latter authors also noticed changes in transcriptional and translational patterns induced by the ELF EM fields in exposed cells. It is important that field strength and frequency- and time-dependent “windows” relative to quantitative changes in specific transcripts were observed [64,65]. Taken together, these features confirm our suggestions concerning the circadian complex-related, pair-radicals-mediated mechanism of biological magnetoreception. Figure 6. Scheme representing possible mechanisms of CRY bio-regulating activity. (a) CLOCK/BMAL1-heterodimer function as transcriptional activator. (b) interaction between CRY1 and CLOCK/BMAL1 causes CLOCK/BMAL1 to adopt a transcriptional repression function. (c) modification of CRY activity by weak external magnetic field and subsequent restoration of CLOCK/BMAL1 transcriptional activation function. CBP: CREB-binding protein. Thus, magnetic fields are able to influence the machinery related to circadian control of gene expression by means of CRY activity modulation. Moreover, it was shown that the CLOCK/BMAL1/CRY1-complex can block promoter activation by other non-circadian transcription factors, working as active transcriptional repressors [60]. The authors showed that daily variations in