EXPRESSION OF GENES INVOLVED IN PHYCOCYANIN BIOSYNTHESIS FOLLOWING RECOVERY OF SYNECHOCOCCUS PCC-6301 FROM NITROGEN STARVATION, AND THE EFFECT OF GABACULINE ON CPCBA TRANSCRIPT LEVELS

The effect of the tetrapyrrole biosynthesis inhibitor gabaculine on th e expression of specific genes involved in phycocyanin biosynthesis wa s investigated in cultures of Synechococcus PCC6301 in nitrogen chloro sis, and during recovery to nitrogen sufficiency. Patterns of transcri ption of the cpcBA (phycocyanin subunits), hemL (glutamate semialdehyd e aminotransferase) and hemB (aminolaevulinate dehydratase) genes were visualised by Northern blotting and gene product formation for cpcBA, hemL and the gene for glu tRNA synthetase were monitored by Western b lotting. Inhibition of phycobilin biosynthesis by gabaculine greatly d ecreased production of phycocyanin protein and of cpcBA transcript, in dicating a tight coordination of apoprotein biosynthesis with chromoph ore supply at the level of transcription. Different patterns of respon se were observed with the other genes at the level of transcript forma tion or gene product synthesis.