Two cDNA clones for the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (SSU) of Batophora oerstedii were isolated and sequenced. One clone contains the coding information for the complete SSU precursor protein. As in two other species of Dasycladaceae (Acetabularia mediterranea and A. cliftonii), the rbcS cDNA sequences of B. oerstedii display the codons TAA or TAG, which seem to code for glutamine, in the reading frame. The amino acid substitution rate for the SSU protein was calculated to be 0.35-0.41 amino acids per 10(9) years per site based on the substitutions observed in the SSU amino acid sequences of Acetabularia and Batophora.

In plant cells a DNA sequence was found which is homologous to the Drosophila per locus. In rape and spinach the homologous sequence occurs in the nuclear but not in the chloroplast genome while in Acetabularia it is found in the chloroplast but not in the nuclear genome. A 1.175 kb EcoRi-SalI fragment of the chloroplast genome of Acetabularia containing the homologous sequence was subcloned into pUC12 and sequenced. The core of the 1.175 kb fragment is a repetitive tandemly arranged sequence of 43 units of the hexamer GGA ACT coding for glycine and threonine.

Labelling of Chlamydomonas reinhardtii cells with [(35)S] methionine led to the detection of a 64-kDa polypeptide which is synthesized according to a circadian rhythm. The change in synthesis rate could be demonstrated to exist under constant dim-light conditions as well as in darkness. Maximum synthesis of the 64-kDa polypeptide occurred at about 10 h after onset of constant conditions, and the period length of its oscillation was about 29 h. The 64-kDa polypeptide was synthesized on 80S ribosomes as shown by experiments in which cycloheximide and chloramphenicol were supplied to the cultures. Peptide-microsequence analysis yielded an N-terminal sequence of 14 amino acids. No significant homology to any other known polypeptide could be demonstrated in searches of current databases. The possible role of the 64-kDa polypeptide and its relationship to the biological clock is discussed.