No abstract

The translation start codon for p&C, the gene encoding CP43, a chlorophyll-binding protein of photosystem II, has been identified for the cyanobacterium Synechosystis sp. PCC 6803 using site-directed mutagenesis. An AUG codon, about 50 bases upstream from the end of psbD-I had previously been assumed to be the translation start site of psbC. However, the fact that the AUG codon is not present in psbC from several other organisms, whereas a GUG codon 14 bases upstream from the end ofpsbD-I is strictly conserved suggests that CP43 translation starts at the latter codon. Mutation of GUG, but not of AUG, led to a loss of CP43 and photoautotrophic growth, indicating that the GUG codon is the sole initiation site for translation of the CP43 protein in Synechocystis sp. PCC 6803.

No abstract

Termination and deletion mutations were introduced near the C-terminal end of the D2 protein in the cyanobacterium Synechocystis sp. PCC 6803 in order to determine the role of the large hydrophilic C-terminal domain of D2 in the function and stability of photosystem II (PS II). The loss of 57 residues from the C-terminal end of D2 (most of the hydrophilic tail) resulted in the loss of D2 and PS II reaction centers from thylakoids. Truncation of 16, 15, 14, or 13 amino acid residues from the C-terminus of D2 resulted in a virtual disappearance of oxygen evolution, a loss of photoautotrophic growth, and a decrease in the number of PS II centers in thylakoids. The loss of 11 C-terminal amino acid residues led to a photoautotrophic mutant that grew at one-half the rate of the wild type under photoautotrophic conditions and that showed a progressive loss of oxygen evolution at high light intensity. Truncation of 9 residues from D2 led to a virtual loss of CP43, presumably because of interference of the mutation with the overlapping ribosome-binding site for psbC translation. To delete smaller portions of D2 and yet not interfere with psbC expression, various deletions were made between the tenth and twentieth amino acid residues from the C-terminal end of D2, resulting in the loss of 8, 7, 4, 3, and 2 residues.(ABSTRACT TRUNCATED AT 250 WORDS)

No abstract