Chlamydomonas transcripts encoding three divergent plastid chaperonins are heat-inducible

Three cDNAs encoding plastid cpn60 chaperonin subunits have been isolated from the unicellular green alga Chlamydomonas reinhardtii. Based on comparisons of the predicted amino acid sequences, we conclude that Chlamydomonas, like higher plants, contains divergent plastid cpn60-α and cpn60-β subunits. The predicted amino acid sequences of the two Chlamydomonas cpn60-β subunits differ significantly (24% divergent), indicating that the two cpn60-β subunits have been selectively maintained for a considerable period of time. Unlike plastid chaperonin trnascripts in higher plants, heat shock conditions (42°C) lead to a rapid increase (10-to 30-fold) in the level of each of the three plastid transcripts.