TARGETED INTERRUPTION OF THE PSAA AND PSAB GENES ENCODING THE REACTION-CENTER PROTEINS OF PHOTOSYSTEM-I IN THE FILAMENTOUS CYANOBACTERIUM ANABAENA-VARIABILIS ATCC-29413
Kj. Nyhus et al., TARGETED INTERRUPTION OF THE PSAA AND PSAB GENES ENCODING THE REACTION-CENTER PROTEINS OF PHOTOSYSTEM-I IN THE FILAMENTOUS CYANOBACTERIUM ANABAENA-VARIABILIS ATCC-29413, Molecular microbiology, 9(5), 1993, pp. 979-988
The two reaction-centre proteins of the photosystem I (PSI) complex ar
e encoded by two adjacent genes named psaA and psaB. We have performed
targeted mutagenesis to insertionally inactivate each of these genes
in the filamentous cyanobacterium Anabaena variabilis ATCC 29413. The
resulting mutant strains, termed psaA::NM(R) and psaB::NM(R), were blu
e because of a high ratio of phycobilin to chlorophyll and were unable
to grow in light. These mutant cells also lacked chemically reducible
P700 (the reaction-centre chlorophylls of PSI) and as a consequence d
id not exhibit any PSI-mediated photochemical activity. However, their
photosystem II (PSII) complexes were fully active. The loss of the Ps
aA and PsaB proteins and their associated chlorophyll molecules result
ed in a five- to sevenfold decrease in the chlorophyll/PSII ratio in t
he mutant cells relative to the wild-type cells. Interestingly, the ps
aB::NM(R) and not the psaA::NM(R) mutant strain retained a small fluor
escence peak (77K) at 721 nm originating from chlorophyll molecule(s)
presumably bound to a small amount of the PsaA protein present in the
psaB mutant. These results demonstrate that this organism is suitable
for the manipulation of PSI reaction-centre proteins.