Transcripts containing the 5' untranslated regions of the plastid genes psbA and psbB from higher plants are unstable in Chlamydomonas reinhardtii chloroplasts.

The 5' regions of chloroplast genes contain cis-acting regulatory elements including promoters, and determinants of RNA stability and translation. In this work I examined whether the 5' regions of the spinach psbB and the wheat psbA genes can drive the expression of an aadA reporter gene in chloroplasts of the unicellar green alga Chlamydomonas reinhardtii. Both plant 5' sequences confer aadA-dependent, spectinomycin resistance on Escherichia coli, but not on the alga following integration into its chloroplast genome. Northern and run-on transcription analyses reveal that the plant promotors are active in C. reinhardtii but that the resulting chimeric transcripts are unstable. Therefore, the data suggest differences between higher plants and green algae with respect to the molecular mechanisms underlying plastid RNA metabolism.