Supplementary Table 1.

Spectroscopic characteristics of holo-subunits formed after attachment of PEB to recombinant R-PE apo-subunits in vivo. From these values and referenced literature [23] it was concluded that attachment of PEB to cells containing R-PE apo-subunits yields holo-subunits containing both urobilin (UB) and PEB.

Phycobilin present in holo-subunit	UB	PEB
Absorption maximum (nm)	496.0	552.0
Excitation fluorescence maximum (nm)	495.0	542.5	569.5
Emission fluorescence maximum (nm)	506.5	573.0	581.5