FIG. 2.

Northern blot analysis of the expression of alr1521 (invA) and alr0819 (invB). RNA isolated from bubbled cultures of Anabaena sp. strain PCC 7120, strain CSE2 (ntcA), and strain 216 (hetR) grown with ammonium (0) and incubated in the absence of combined nitrogen for the times indicated in hours was electrophoresed and hybridized with the probes indicated at the left, which were generated by PCR (see Materials and Methods). The positions of some size markers are indicated at the right. Hybridization with an rnpB gene probe was used as a loading and transfer control.