How do chromophytic algae regulate chloroplast gene expression?
Sequence analysis of the Heterosigma chloroplast genome revealed the presence of a single two-component His-to-Asp (tsg1/Trg1) pair in this golden-brown alga. Our data represent the first documentation of His-to-Asp arrays in chromophytic algae and counter previous reports suggesting that such regulatory proteins are lacking in the stramenopile taxonomic cluster. Molecular modeling of the 27 kd Heterosigma Trg1 regulator protein is consistent with a winged helix-turn-helix identity–a class of proteins that is known to impact gene expression at the level of transcription. Our data support the hypothesis that the response regulators of chromophytes, rhodophytes, and glaucophytes interact with a sigma 70 subunit (encoded by rpoD) of a eubacterial type polymerase. rpoD has now been sequenced in Heterosigma. Both transcriptional and western analysis verify that tsg1 is not a pseudogene. We hypothesize that tsg1 is red/ox regulated. tsg1/trg1 pair is phylogenetically constrained in its dist
