THE STRUCTURE OF PHYCOBILISOMES IN MUTANTS OF SYNECHOCOCCUS SP STRAINPCC-7942 DEVOID OF SPECIFIC LINKER POLYPEPTIDES

The effect of elimination of the 30, 33 and 9 kDa phycobilisome rod-li nker polypeptides on rod length was examined by electron microscopy of phycobilisomes isolated from wild-type Synechococcus sp. strain PCC 7 942 and from genetically engineered mutants with lesions in the genes encoding the rod-linker polypeptides. The maximum rod length in the ab sence of the 33 kDa linker polypeptide was two phycocyanin hexamers, w hereas rods with up to five hexamers were found in the mutant strain l acking the 30 kDa linker polypeptide. Elimination of the 9 kDa linker polypeptide did not have a significant effect on rod length. Finally, mutants lacking either the 30 or 33 kDa rod-associated linker polypept ides had an increased number of rods that terminated with a phycocyani n trimer. These observations are discussed with respect to the role of the linker polypeptides in the biosynthesis of the rod substructure.