The flanking regions of PsaD drive efficient gene expression in the nucleus of the green alga Chlamydomonas reinhardtii

The nuclear gene PsaD encodes an abundant chloroplast protein located on th e stromal side of the Photosystem I complex. We have cloned and sequenced a genomic fragment containing the PsaD gene from the green alga Chlamydomona s reinhardtii. Sequence comparison with its cDNA revealed that the PsaD ORF contains no introns. Thus, the regulatory sequences required for high-leve l expression of PsaD must lie in the flanking promoter and untranslated reg ions. We used this genomic fragment to construct a vector that allows for h igh-level expression of endogenous and exogenous genes, as well as cDNAs th at could not be expressed from existing vectors. It is also possible to use the PsaD transit sequence to target the expressed protein to the chloropla st compartment.