Cd. Carrasco et al., PROGRAMMED DNA REARRANGEMENT OF A CYANOBACTERIAL HUPL GENE IN HETEROCYSTS, Proceedings of the National Academy of Sciences of the United Statesof America, 92(3), 1995, pp. 791-795
Programed DNA rearrangements that occur during cellular differentiatio
n are uncommon and have been described in only two prokaryotic organis
ms. Here, we identify the developmentally regulated rearrangement of a
hydrogenase gene in heterocysts of the cyanobacterium Anabaena sp. st
rain PCC 7120. Heterocysts are terminally differentiated cells special
ized for nitrogen fixation. Late during heterocyst differentiation, a
10.5-kb DNA element is excised from within the hupL gene by site-speci
fic recombination between 16-bp direct repeats that flank the element.
The predicted HupL polypeptide is homologous to the large subunit of
[NiFe] uptake hydrogenases. hupL is expressed similarly to the nitroge
n-fixation genes; hupL message was detected only during the late stage
s of heterocyst development. An open reading frame, named xisC, identi
fied near one end of the hupL DNA element is presumed to encode the el
ement's site-specific recombinase. The predicted XisC polypeptide is h
omologous with the Anabaena sp. strain PCC 7120 site-specific recombin
ase XisA. Neither XisC nor XisA shows sequence similarity to other pro
teins, suggesting that they represent a different class of site-specif
ic recombinase.