CHLAMYDOMONAS TRANSCRIPTS ENCODING 3 DIVERGENT PLASTID CHAPERONINS ARE HEAT-INDUCIBLE

Three cDNAs encoding plastid cpn60 chaperonin subunits have been isola ted from the unicellular green alga Chlamydomonas reinhardtii. Based o n comparisons of the predicted amino acid sequences, we conclude that Chlamydomonas, like higher plants, contains divergent plastid cpn60-al pha and cpn60-beta subunits. The predicted amino acid sequences of the two Chlamydomonas cpn60-beta subunits differ significantly (24% diver gent), indicating that the two cpn60-beta subunits have been selective ly maintained for a considerable period of time. Unlike plastid chaper onin transcripts in higher plants, heat shock conditions (42 degrees C ) lead to a rapid increase (10- to 30-fold) in the level of each of th e three plastid transcripts.