Three light-inducible heat shock genes of Chlamydomonas reinhardtii.

Genomic clones representing three Chlamydomonas reinhardtii genes homologous to the Drosophila hsp70 heat shock gene were isolated. The mRNAs of genes hsp68, hsp70, and hsp80 could be translated in vitro into proteins of Mr 68,000, 70,000, and 80,000, respectively. Transcription of these genes increased dramatically upon heat shock, and the corresponding mRNAs rapidly accumulated, reaching a peak at around 30 min after a shift to the elevated temperature. Light also induced the accumulation of the mRNAs encoded by these heat shock genes. A shift of dark-grown cells to light resulted in a drastic increase in mRNA levels, which reached a maximum at around 1 h after the shift. Thus, in Chlamydomonas, expression of hsp70-homologous heat shock genes appears to be regulated by thermal stress and light.