Stabilization and translation of the psbD mRNA
in Chlamydomonas reinhardtii

Nickelsen, J., Rochaix, J.-D., Ossenbuehl, F., Tourne, H.

LS Allgemeine Botanik, Ruhr-University Bochum, Universitätsstr. 150, D-44780 Bochum, Germany

Chloroplast gene expression has been shown to be regulated at various levels including transcription and, more important, posttranscriptional steps like mRNA stabilization, processing and translation. Several lines of evidence suggest that these processes are controlled by nucleus-encoded factors that interact with distinct cis-elements on chloroplast RNAs to fulfill their function. The analysis of the nuclear Chlamydomonas reinhardtii mutant nac2-26, deficient in psbD mRNA accumulation, revealed that the principal target site for the affected nucleus-encoded factor is located within the 5´ leader region of the psbD transcript (Nickelsen et al., 1994, EMBO J. 13, 3182-3191). By using biolistic chloroplast transformation several mutations were introduced into the endogenous psbD 5´ region. These mutations identify two critical elements required for the stabilization of the psbD mRNA, while its translation is affected by changing sequences downstream of these elements and by alterations of the ATG start-codon. In order to characterize the trans-acting factors involved in psbD gene expression, in vitro RNA-binding experiments were performed which suggest, that a 47 kDa protein, specifically interacting with the psbD leader, plays a role for RNA stabilization. Furthermore, the NAC2-26 locus was cloned based on the complementation of the photosynthetic mutant. The polypeptide sequence derived from the cDNA exhibits a TPR (Tetratricopeptide) domain and a C-terminal hydrophobic tail. This suggests that psbD mRNA stabilization might be mediated by a membrane-associated multisubunit complex. This work is supported by the Deutsche Forschungsgemeinschaft (Ni390/2-1).

LOCATION DATE TIME
Lecture Hall I Thursday, April 9 04:50 pm