2 ANABAENA SP STRAIN PCC 7120 DNA-BINDING FACTORS INTERACT WITH VEGETATIVE CELL-SPECIFIC AND HETEROCYST-SPECIFIC GENES

The DNA-binding factor BifA (previously called VF1) binds upstream of the developmentally regulated site-specific recombinase gene xisA in t he cyanobacterium Anabaena sp. strain PCC 7120. Besides binding xisA, BifA also binds the glnA, rbcL, and nifH promoter regions. DNase I foo tprint analysis of BifA binding to glnA showed a protected region -125 to -148 bp upstream of the translation start site. The binding site i s between the major glnA transcription start site used in vegetative c ells (RNA(II)) and the major transcription start site used under nitro gen-deficient conditions (RNA(I)). The two BifA-binding sites on the r bcL promoter were localized to a 24-bp region from +12 to -12 nucleoti des and to a 12-bp region from -43 to -54 nucleotides with respect to the transcription start site. Comparison of the BifA binding sites on the glnA, xisA, and rbcL upstream regions revealed the consensus recog nition sequence TGT(N-9 or 10) ACA. We have identified a second DNA-bi nding activity (factor 2) that interacts with rbcL and xisA upstream r egions. Factor 2 can be resolved from BifA by heparin-Sepharose chroma tography and was present in a bifA mutant. Analysis of partially purif ied vegetative cell and heterocyst extracts showed that whereas BifA w as present in both cell types, factor 2 was present only in vegetative cells. DNase I footprint analysis of factor 2 binding to rbcL showed protection of a 63-bp region between positions -15 and -77 with respec t to the transcription start site. The factor 2 binding site on xisA w as localized to a 68-bp region that showed considerable overlap with t he BifA binding sites.