Cc. Bauer et al., SUPPRESSION OF HETEROCYST DIFFERENTIATION IN ANABAENA PCC-7120 BY A COSMID CARRYING WILD-TYPE GENES ENCODING ENZYMES FOR FATTY-ACID SYNTHESIS, FEMS microbiology letters, 151(1), 1997, pp. 23-30
A cosmid containing a wild-type Anabaena PCC 7120 DNA fragment was fou
nd to suppress heterocyst differentiation, creating a Het phenotype in
an otherwise wild-type strain. Curing of the cosmid restored the full
wild-type Het(+) Nif(+) phenotype. The cosmid contains at least four
genes encoding proteins with significant sequence similarity to enzyme
s involved in the synthesis of fatty acids. Selection for Nif(+) rever
tants of the suppressed strain yielded modified cosmids, one of which
contained a 10.2-kb transposon, Tas1, inserted into the promoter regio
n of a gene encoding a protein with acyl carrier and beta-keto reducta
se domains. This gene, called hetN, was shown previously by Black and
Wolk (J. Bacteriol. (1994) 176, 2282-2292) to inhibit heterocyst diffe
rentiation when present alone on a plasmid. Oddly, hetN gene transcrip
tion is detected later than 6 h into heterocyst differentiation.