Research letterCotranscription of the large and small subunit genes of ribulose-1,5-bisphosphate carboxylase/oxygenase in Cyanophora paradoxa

The region of the cyanelle genome of Cyanophora paradoxa which codes for ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBis-CO) has been cloned and partially characterized. The large subunit gene (rbcL) is located adjacent to, and upstream from the small subunit gene (rbcS). The rbcS, containing 318 nucleotides, codes for a polypeptide that exhibits greater homology to small subunits of cyanobacteria than to those of angiosperms. Immediately downstream from the rbcS termination codon is an apparent transcription termination site consisting of an inverted repeat followed by a T cluster. The spacer region separating rbcL and rbcS is 105 nucleotides in length and lacks an obvious RNA polymerase promoter sequence suggesting that the genes are cotranscribed. Northern blot analysis has confirmed the cotranscription of both genes as a single transcript of approx. 2500 nucleotides.