Quantitative analysis of expression of two circadian clock-controlled geneclusters coding for the bidirectional hydrogenase in the cyanobacterium Synechococcus sp PCC7942

Hydrogen metabolism is of central interest in cyanobacterial research becau se of its potential applications. The gene expression and physiological rol e of the cyanobacterial bidirectional NAD(P)(+)-reducing hydrogenase are po orly understood. Transcription rates of hoxEF and hoxUYH encoding this enzy me have been studied in Synechococcus sp. PCC7942. P-hoxU activity was abou t three times higher than that Of P-hoxE. Circadian phasing of both promote rs was found to be synchronous and influenced expression levels by at least one order of magnitude. This is the first demonstration of circadian contr ol of gene expression for any hydrogenase. For the majority of P-hoxU-drive n messages, transcription presumably terminates between hoxU and hoxH. Bein g part of a polycistronic hoxUYHW... operon, hoxW, encoding a protease invo lved in C-terminal processing of the hydrogenase large-subunit HoxH, is mai nly expressed by its own promoter, P-hoxW. The complex transcript formation may be a key feature for controlling bidirectional hydrogenase expression in vivo.