FIG. 1.

(A) Physical map of the hox gene clusters (depicted in black) in Nostoc sp. strain PCC 7120. ORFs present on the same transcript as the hox genes are depicted in gray, and the ORF corresponding to the putative bidirectional-hydrogenase-specific C-terminal endopeptidase, hoxW (all0770), is striped. (B) RT-PCR analysis of the two hox gene clusters. Total RNA was isolated from cells grown under dark, anaerobic conditions for 24 h. The RT reactions were performed with primers against hoxF, followed by PCRs for alr0750, hoxE, hoxF, and hoxH, followed by PCRs for alr0760, alr0761, hoxU, alr0763, hoxY, alr0765, and hoxH (primers are listed in Table 1). Lanes: a, RT-PCR product; b, negative control without reverse transcriptase in the RT reaction prior to the PCR; c, PCR-positive control; marker, 100-base-pair ladder (Amersham Biosciences) where the lowest visible band corresponds to 100 base pairs.