The function of the RNA binding protein CHLAMY1 in the circadian clock and its temperature integration process The research of this thesis focused on the circadian RNA binding protein CHLAMY1 from the green alga Chlamydomonas reinhardtii that consists of two subunits C1 and C3. CHLAMY1 binds specifically to (UG)7 repeat sequences situated in the 3 UTRs of several mRNAs such as nitrite reductase 1 (nii1). The role of the C1 subunit within the circadian system was characterized by silencing its gene by an RNAi. The expression level of C1 was silenced down to 25 85%. To show the influence of CHLAMY1 on circadian output NII activities were measured. In wild type NII activity peaks around the beginning of subjective day. In the transgenic strain arrhythmicity was observed. Circadian phototaxis was chosen as a second output rhythm. In this case arrhythmicity was observed immediately or in the first three days under constant conditions in transgenic lines. In addition to these results a co regulation between C1 and C3 subunits was found. These data indicate a central role of the C1 subunit in the circadian system of C. reinhardtii. It was also analyzed if the two subunits play a role in temperature integration. C1 was found to be hyper phosphorylated at 18ʿC and hypo phosphorylated at 28ʿC. The C3 expression level was found to be up regulated at 18ʿC which was shown to occur at the transcriptional level. The clock relevant CASEIN KINASE1 (CK1) and Ser Thr PROTEIN PHOSPHATASEs (PPs) were found to mediate the temperature dependent regulation of C1 and C3. The expression of CK1 was itself temperature controlled and increased at 28ʿC. In the long period clock mutant per1 temperature integration of both C1 and C3 was shown to be altered: a low phosphorylation level of C1 and a high expression level of C3 was observed at different temperatures. Altogether the data suggest that a temperature controlled functional network of clock relevant proteins exists in C. reinhardtii including C1 C3 CK1 PPs and PER1.