FIG. 4.

The region of cyanobacterial DNA that complements the nblB mutant phenotype. (A) The complementing plasmid linearized with BamHI (B). The plasmid contains a 9.7-kbp insert of which a 2.7-kbp ClaI (C)/SacII (S) fragment, enlarged and to the left of the vector sequence, is capable of complementing the mutant phenotype. The positions of ORF1, ORF2, ORF3, and ORF4 (or nblB) on the fragment are indicated. ORF1 is truncated at the 5′ end, while the remaining ORFs are complete. A restriction site for EcoRI (E) is also shown. The ORFs were individually inactivated by insertion of the Ω cassette at the BsrGI site (Bs) of ORF1, the BglI site (Bg) of ORF2, and the NheI site (N) of ORF3. ORF4 or nblB was interrupted by deletion of an XhoII fragment followed by insertion of the Ω cassette. (B) Effect of inactivation of each of the four ORFs on bleaching during sulfur (−S) and nitrogen (−N) limitation.