Surface plasmon resonance spectroscopy (SPR) interaction studies of the circadian-controlled tomato LHCa4*1 (CAB 11) protein with its promoter.

Feedback regulation is an important biochemical mechanism which is also able to direct the circadian timing at the transcriptional level. Independent investigations highlighted a conserved ca. 10 nucleotide motif present in many circadian regulated Lhc genes. Two of such nucleotide motifs exist within 119 nucleotides of the Lhca41 promoter from tomato. This promoter fragment was used as a bait in a yeast one hybrid screen and interestingly a clone encoding with sequence identity to the LHCa41 protein was isolated as an interaction partner. The LHCa41 protein was heterologous expressed and binding to the 119bp promoter fragment was demonstrated by surface plasmon resonance spectroscopy (SPR, Biacore). This result allows to postulate an autoregulatory feedback loop involved in expression of the Lhca41 gene.