Blue light-dependent regulator that is the input of the circadian feedback loop. Has no photolyase activity for cyclobutane pyrimidine dimers or 6-4 photoproducts. Regulation of expression by light suggests a role in photoreception for locomotor activity rhythms. Light induces the degradation of cry, likely due to conformational change in the photoreceptor leading to targeting to the proteasome. Under circadian regulation, expression is influenced by the clock pacemaker genes period, timeless, Clock and cycle. Binding to tim irreversibly commits tim to proteasomal degradation. Functions, together with per, as a transcriptional repressor required for the oscillation of peripheral circadian clocks and for the correct specification of clock cells. Genes directly activated by the transcription factors Clock (Clk) and cycle (cyc) are repressed by cry. Necessary for light-dependent magnetosensitivity, an intact circadian system is not required for the magnetoreception mechanism to operate. Required for both the naive and trained responses to magnetic field, consistent with the notion that Cry is in the input pathway of magnetic sensing (By similarity). Binds 1 FAD per subunit. Interacts with tim and per; promoted by light conditions. Nuclear translocation initiates after the perception of a light signal. Accumulates in the perinuclear region about one hour before translocation into the nucleus. Translocation occurs through interaction with other Clock proteins such as tim and per (By similarity). FAD-binding region regulates cry stability, cry-tim interaction, and circadian photosensitivity. Photolyase/cryptochrome alpha/beta domain is sufficient for light detection and phototransduction. Belongs to the DNA photolyase class-1 family.