Isolation and characterization of novel genes which are expressed during the very early stage of zygote formation in Chlamydomonas reinhardtii.

We have obtained five cDNA clones which are complementary to transcripts that accumulate specifically during the early stage of zygote formation in Chlamydomonas reinhardtii. Based on the time-course of transcript accumulation of their corresponding genes, these clones were classified into two groups: an early expression group (three clones; pZS102-1, pZS102-69, pZS1802) and a late expression group (two clones; pZS1860 and pZS1886). The levels of transcripts in the former group reached a maximum 30 min after the onset of mating, whereas those in the latter group peaked at 3 h. The addition of 10 micrograms/ml of cycloheximide reduced the decline in the levels of transcripts, except in the transcript corresponding to pZS102-69. Two clones, pZS102-1 and pZS102-69, contained highly-homologous predicted open-reading frames, and were judged to be cDNAs for two members of a novel gene family. These genes were referred to as zys1A and zys1B, respectively.