NUCLEOTIDE-SEQUENCE AND EXPRESSION OF THE GENES FOR THE ALPHA-SUBUNITAND BETA-SUBUNIT OF PHYCOCYANIN IN CYANIDIUM-CALDARIUM

The nucleotide sequence of the plastid-encoded operon containing genes for the alpha (cpcA) and beta (cpcB) subunits of phycocyanin in the u nicellular red alga Cyanidium caldarium is described. cpcB is located 5' to cpcA and the two genes are separated by a 102-bp spacer region. The transcription start site of cpcBA was mapped to 80 bp upstream of the ATC initiation codon of cpcB. Promoter-like elements similar to th e -10 (TATAAT) and -35 (TTGACA) consensus promoters in bacteria were f ound 6 and 31 bp upstream of the transcription initiation site. Northe rn blotting revealed an abundant 1.3-kb cpcBA transcript in illuminate d cells, but this transcript was undetectable in dark-grown cells. Exp ression levels of cpcBA in cells incubated with 10-6 10(-6) M heme in the dark were similar to those in cells illuminated for 24 h. Cells il luminated with 150 mu M gabaculine (an inhibitor of delta-aminolevulin ate synthesis) or 10 mM levulinic acid (an inhibitor of delta-aminolev ulinate dehydrase) lacked detectable cpcBA transcripts. In cells illum inated with 200 mu M N-methylmesoporphyrin IX (an inhibitor of ferroch eletase), inhibition of cpcBA expression and phycocyanin synthesis was similar. These results provide strong evidence that light induction o f the cpcBA operon is dependent on synthesis of heme.