ABSTRACT
Circadian rhythms control the temporal arrangement of molecular, physiological,
and behavioral processes within an organism and also synchronize these
processes with the external environment. A cell autonomous molecular
oscillator, consisting of interlocking transcriptional/translational
feedback loops, drives the approximately 24-hour duration of these
rhythms. The cryptochrome protein (CRY) plays a central part in the
negative feedback loop of the molecular clock by translocating to the
nucleus and repressing CLOCK and BMAL1, two transcription factors that
comprise the positive elements in this cycle. In order to gain insight
into the inner workings of this feedback loop, we investigated the
structure/function relationships of Xenopus laevis CRY1
(xCRY1) and xCRY2 in cultured cells. The C-terminal tails of both xCRY1
and xCRY2 are sufficient for their nuclear localization but achieve it
by different mechanisms. Through the generation and characterization of
xCRY/photolyase chimeras, we found that the second half of the
photolyase homology region (PHR) of CRY is important for repression
through facilitating interaction with BMAL1. Characterization of these
functional domains in CRYs will help us to better understand the
mechanism of the known roles of CRYs and to elucidate new intricacies
of the molecular
clock.
Molecular characterization of a second iron-responsive element binding protein, iron regulatory protein 2. Structure, function, and post-translational regulation.
