TABLE 1.

Cyanobacterial strains and plasmids used in this study

Strain or plasmid	Relevant characteristics	Reference or source
Strains
PCC 7120	Wild-type Anabaena strain	26
EF116	Derivative of Anabaena sp. strain PCC 7120 unable to fix nitrogen under oxic conditions	47
CSE27	Derivative of EF116 with a deletion in the nirA gene	10
CSE36	Smr Spr derivative of strain EF116; nrtB::C.S3	This work
CSE38	Smr Spr derivative of strain PCC 7120; narM::C.S3	This work
CSE39	Derivative of strain PCC 7120; Δalr0613	This work
CSE40	Derivative of strain PCC 7120; ΔnarB	This work
Plasmids
pCSE139	1,618-bp product of PCR with primers narB-7120-5 and alr0614-3, cloned in pGEM-T	This work
pCSE140B	pCSE139 insert bearing EcoRI-ended gene cassette C.S3 (39) inserted into the EcoRI site of narM, cloned in pRL271; used to generate mutant strain CSE38	This work
pCSE148	2.0-kb BspHI/SphI fragment from pCSE26 (8) cloned in NcoI/SphI-digested pCSAM170 (48); it overproduces His-tagged Anabaena NirA protein	This work
pCSE153B	2.9-kb ClaI/XbaI fragment from pCSE2 (8) bearing HincII-ended gene cassette C.S3 inserted into the ScaI site of nrtB, cloned in pRL278; used to generate mutant strain CSE36	This work
pCSE174B	1,265-bp product of PCR with primers narB-7120-5, alr0613-5, alr0613-6, and alr0614-3, with pCSE39 as the template; presents a deletion of a 351-bp internal segment of alr0613, corresponding to nucleotides 36 to 386 of the 459-nucleotide coding region; cloned in pRL277; used to generate mutant strain CSE39	This work
pCSE189	PCR fragment amplified using primers narB-7120-8 and narB-7120-11, cloned in pKT25 using XbaI and KpnI; it produces the T25-NarB hybrid protein	This work
pCSE191	Derivative of pUT18C; it presents restriction site XbaI in a polylinker replaced by restriction site NcoI, using primers pUT18-3 and pUT18-4	This work
pCSE192	Derivative of pKT25; it presents restriction sites SalI and KpnI in a polylinker replaced by restriction sites BspHI and SphI, respectively, using primers pKT25-3 and pKT25-4	This work
pCSE193	2.0-kb BspHI/EcoRV fragment from pCSE26 cloned in pCSE192 using BspHI and SmaI; it produces the T25-NirA hybrid protein	This work
pCSE195	1,716-bp product of PCR with primers orf398-7120-5 and all0604-2 (10), cloned in pCSE191 using NcoI and ClaI; it produces the T18-NirB hybrid protein	This work
pCSE200	As for pCSE193, but cloned in pCSE191 using NcoI and SmaI; it produces the T18-NirA hybrid protein	This work
pCSE201	Insert of pCSE195 cloned in pCSE192 using BspHI and SmaI; it produces the T25-NirB hybrid protein	This work
pCSE242	PCR fragment amplified using primers alr0614-9 and alr0614-10, cloned in pUT18 using PstI and EcoRI; alr0614-9 also allows elimination of the EcoRI site internal to narM without changing the NarM amino acid sequence; it produces the T18-NarM hybrid protein	This work
pCSE243	As for pCSE242, but cloned in pUT18C using PstI and EcoRI; it produces the NarM-T18 hybrid protein	This work
pCSE245	narB gene with a deletion of the internal 588-bp PvuII fragment, cloned in pRL277; used to generate mutant strain CSE40	This work
pCSE246	As for pCSE189, but cloned in pKNT25 using XbaI and KpnI; it produces the NarB-T25 hybrid protein	This work
pRL277	Smr Spr, sacB-carrying, mobilizable vector	49
pRL278	Nmr, sacB-carrying, mobilizable vector	49
pRL443	Kms derivative of conjugative plasmid RP4	30
pRL623	Mobilization helper; encodes M.AvaI, M.Eco47II, and M.EcoT22Ia	31
pUT18	Plasmid used for BACTH analysis	28
pUT18C	Plasmid used for BACTH analysis	28
pKT25	Plasmid used for BACTH analysis	28
pKNT25	Plasmid used for BACTH analysis	28

^aM, methylase.