ISOLATION AND CHARACTERIZATION OF BACILLUS-SUBTILIS GENOMIC LACZ FUSIONS INDUCED DURING PARTIAL PURINE STARVATION

Random genomic Bacillus subtilis lacZ fusions were screened in order t o identify the possible existence of regulons responding to the stimul i generated by partial purine starvation. A leaky pur mutation (purL8) was isolated and used to generate the partial purine starvation condi tions in the host strain used for screening. On the basis of their ind uction during partial purine starvation, seven genomic lacZ fusions we re isolated. None of the fusions map in loci previously reported to co ntain purine-regulated genes. One fusion maps very close to the citB l ocus and may very well be a citB fusion. The fusions were divided into two types on the basis of their response to complete starvation for e ither ATP or GTP or both components at the same time. Except for one, type 2 fusions were induced by specific starvation for ATP and by simu ltaneous starvation for ATP and GTP, but not by specific GTP starvatio n in a gua strain or by GTP starvation induced by the addition of deco yinine. Type 1 fusions were equally well induced by all three kinds of purine starvation including GTP starvation induced by decoyinine. Fur ther subdivisions of the fusions were obtained on the basis of their r esponses to the spo0A gene product. A total of five fusions showed tha t spo0A affected expression. One class was unable to induce lacZ expre ssion in the absence of the spo0A gene product, whereas the other clas s had increased lacZ expression during partial purine starvation in a spo0A background.