FIG 4.

The metE promoter from Synechococcus sp. strain PCC 73109 contains a putative cobalamin riboswitch. (A) Representation of P_metE in plasmid pAQ3Ex-P_metE[yfp]. (B) Detection of YFP expression in strain AAP003. Fluorescence emission spectra of YFP in vivo with Synechococcus sp. strain PCC 7002 normalized at an OD₇₃₀ of 1.0 in growth medium A⁺ with or without exogenous cobalamin. The dotted line shows fluorescence emission from WT Synechococcus sp. strain PCC 7002 grown in medium A⁺ as a negative control. The dashed line shows YFP fluorescence emission in strain AAP003 in the presence of cobalamin in A⁺ medium, and the solid line shows YFP fluorescence emission for the same strain grown in medium A⁺ B₁₂^–.