FIG. 4.

Transcript analysis of vupAB. (A and B) For Northern blot assays of vupA and vupB transcripts, RNA was isolated from cultures of A. variabilis grown in AA/8 with or without Mo or V and was hybridized with ³²P-labeled probes to vupA (A) or vupB (B) as described previously (55). +Mo, with molybdate; +V, Mo-free medium with V; =, Mo- and V-free medium. Arrows indicate sizes of the hybridizing bands. The lower parts of panels A and B show the hybridization signal with a probe for the constitutively expressed rnpB gene (52). (C) RT-PCR performed with RNA isolated from cells grown in Mo-free AA/8 with vanadate (lanes 1 and 2), with molybdate (lanes 3 and 4), or in Mo-free AA/8 with NH₄Cl to repress heterocysts (lanes 5 and 6). Lanes 1, 3, and 5 contained complete RT-PCR reagents. Control reactions shown in lanes 2, 4, and 6 lacked only reverse transcriptase. The PCR product made from DNA with the WabcA primers is shown in lane 7. The control reaction mixture shown in lane 8 had no template. The markers shown in lane M were Bioline Hyperladder IV (100 to 1,000 bp).