ISOLATION,CHARACTERIZATION AND RECONSTITUTION OF PHYCOBILIPROTEIN ROD-CORE LINKER POLYPEPTIDE COMPLEXES FROM THE PHYCOBILISOME OF Mastigocladus laminosus*

A rod-core complex, (αβ)₆^PC. L_RC^29.5,(αβ)₃^APC.L_C^8.9, composed of hexameric phycocyanin (PC) and trimeric allophycocyanin (APC) subcomplexes associated to the CpcG2 gene product, has been isolated from the phycobilisome of Mastigocladus laminosus. Exactly the same complex was obtained by reconstitution using the subcomplexes(αβ)₃^PC. L_RC 29.5 and (aβ)₃^APC.L_C^8.9 as educts. Spectroscopic analysis of the isolated PC-L_R and PC-L_RC complexes from M. laminosus shows that the L_RC cause the largest red-shift in the absorbance and fluorescence emission maxima of PC. These results indicate that L_RC mediate PC-APC interactions in vitro. Only the CpcG2 polypeptide was able to promote this specific interaction, as neither CpcG3-PC nor, as a negative control, CpcC-PC complexes showed any reconstitution products with the core subcomplex (αβ)₃^APC.L_c^8.9. This is an indication that each of the four L_RC in the phycobilisomes of M. laminosus and Anabaena sp. PCC 7120 attaches two peripheral rods specifically to one of four different core binding sites.