ANABAENA-XISF GENE ENCODES A DEVELOPMENTALLY-REGULATED SITE-SPECIFIC RECOMBINASE

Two DNA elements are excised from the chromosome during Anabaena heter ocyst differentiation. We have identified the gene xisF which encodes the site-specific recombinase responsible for the excision of a 55-kb element from within the fdxN gene. The cloned xisF gene is sufficient to cause site-specific rearrangement of an artificial substrate in Esc herichia coli. Inactivation of xisF in the Anabaena chromosome prevent s excision of the fdxN element and growth in nitrogen-deficient medium but does not alter the development of heterocysts. Forced transcripti on of xisF in vegetative cells did not result in excision of the fdxN element, suggesting that other factors may be involved in cell-type sp ecificity. The predicted XisF protein shows significant similarity to the Bacillus subtilis SpoIVCA recombinase.