A screen for sequences up-regulated during heterocyst development in Anabaena sp strain PCC 7120

A plasmid library of small genomic fragments from the cyanobacterium Anabae na sp. strain PCC 7120 was screened for sequences whose transcripts increas e in abundance during a heterocyst development time course. A total of 350 clones were analyzed, representing 1-2% of the Anabaena sp, strain PCC 7120 genome. Twenty-seven clones (8%) showed some degree of up-regulation after nitrogen starvation. The increase in transcript abundance ranged from 1.2- fold to 3.5-fold. Further analysis of the expression of some of the sequenc es using Northern blots suggested that. the up-regulation values calculated from the screen are underestimates. The collection of upregulated clones i ncludes novel genes, previously characterized genes, and genes identifiable by similarity to known genes. One of the novel genes has been shown to be required for heterocyst function, and the sequence similarities and, expres sion patterns of some of the others suggest that they may play a role in he terocyst development.