Figure 3

Analysis of the nifB-fdxN-nifS-nifU operon structure, 5' end, and expression levels in response to nitrogen deprivation. RNA-seq read coverage is shown on a log scale across the nifB-fdxN-nifS-nifU operon in heterocyst chromosomes for 0, 6, 12, and 21 hours after the removal of combined nitrogen. The log scale is required to allow depiction of both the low numbers of reads at earlier time points and the large increase in reads at 21 h. The 59,428-bp fdxN element (denoted by the gray triangle) is excised from the chromosome in heterocysts [6], and the break in nucleotide numbering for the vegetative-cell chromosome is marked with «». The position of the previously mapped mRNA 5' end for the operon is at 282 bases upstream of the nifB start codon (marked by the black downward arrow in the 21 h graph) [30].