CLONING, SEQUENCING AND TRANSCRIPTIONAL STUDIES OF THE GENES FOR CYTOCHROME C-555 AND PLASTOCYANIN FROM ANABAENA SP PCC-7120

In some cyanobacteria and eukaryotic algae, cytochrome c-553 (c-552) a nd plastocyanin function as alternative electron carriers between the cytochrome b(6)-f complex and Photosystem I. In these organisms plasto cyanin is the electron carrier under copper-replete conditions, and cy tochrome c-553 is the electron carrier during copper deprivation. In t his paper we report the cloning, sequencing and transcriptional analys is of the genes for cytochrome c-553 and plastocyanin from Anabaena sp . PCC 7120. The gene for cytochrome c-553 encodes a preprotein contain ing 111 amino acids with a predicted N-terminal transit peptide sequen ce of 25 amino acids. The gene for plastocyanin encodes a preprotein c ontaining 139 amino acids with a N-terminal transit peptide sequence o f 34 amino acids. RNA transcript analyses indicate that the expression of the genes for cytochrome c-553 (petJ) and plastocyanin (petE) are regulated in reciprocal ways in response to copper concentration. In c opper-replete conditions, petJ is expressed at very low levels, but is transcribed at high levels under copper deprivation; petE is down-reg ulated in the absence of copper, but is rapidly up-regulated when copp er is added back to the medium.