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 |