Though, it becomes more and more clear that coupling the PTO with the TTFL is essential under certain conditions, for example to gain synchronous oscillations in a population of growing cells ( Teng 3-Methyladenine in vitro et al., 2013). We would go beyond the scope of this review to recapitulate all the studies and rather refer the reader to the following

interesting articles: Kitayama et al., 2008, Qin et al., 2010b, Teng et al., 2013, Yang et al., 2010 and Zwicker et al., 2010. The internal circadian clock maintains an endogenous rhythm of about 24 h that is governed by the period length of the oscillator. The free-running period of the endogenous oscillator is determined genetically and is close to but not equal to 24 h. In order to measure the time precisely, the clock has to be synchronized to the exact 24-hour cycle of the Earth rotation. There are several external signals that oscillate in the natural environment and that can serve PLX4032 datasheet as a real-time cue (Zeitgeber). Known Zeitgeber are the daily light–dark cycles as well as temperature (Liu et al., 1998) or food availability (Damiola et al., 2000). In eukaryotic circadian systems usually a photoreceptor is involved in entrainment of the internal oscillator. Here, cryptochrome is a major player with different mechanisms of function in various organisms. In Mammals, two cryptochromes belong to the core of the molecular clock (Ko and Takahashi, 2006) whereas in Drosophila a cryptochrome is the major circadian photoreceptor

( Emery et al., 1998). Cyanobacteria harbor many different photoreceptors including cryptochromes and various types of phytochromes. Nevertheless, none of the putative photoreceptors identified in S. elongatus by genome analysis was found to be involved in clock functions ( Mackey et al., 2011). Therefore it was speculated that the photosynthetic antennae can serve as a megaphotoreceptor to synchronize the cyanobacterial clock. However, other components of the input pathway have been identified for the S. elongatus clock. Fig. 1A depicts the molecular mechanisms of the circadian clock in S. elongatus. So far, there are three

major players of the input pathway, which sense either changes in the redox state of the electron transport chain (circadian input kinase A, CikA; light dependent period, LdpA) or are regulated directly http://www.selleck.co.jp/products/Neratinib(HKI-272).html by light (period extender, Pex) ( Ivleva et al., 2005, Kutsuna et al., 1998 and Schmitz et al., 2000). Further, four proteins were identified, namely NhtA, PrkE, IrcA, and CdpA that may help connecting CikA with the circadian central oscillator ( Mackey et al., 2008). CikA has a protein histidine kinase domain as typically found in sensor kinases of bacterial two-component signal transduction systems. Though CikA contains an N-terminal GAF domain and has some homologies to phytochrome photoreceptors it does not bind a bilin as a chromophore ( Mutsuda et al., 2003). Interestingly, the CikA homolog from the freshwater strain Synechocystis sp.