During sporulation, Bacillus subtilis undergoes successive morphological changes that can be arrested at various stages by mutations in many genes. One of these, spollGB, encodes a transcriptional factor, cr ~, which is necessary to proceed beyond stage II and to differentiate the cell in two compartments, the forespore and the mother cell. Mutations were introduced in an open reading [tame located immediately downstream of spollGB. They block sporulation at stage III and define a new gene, spolllG, encoding a 260-amino-acid polypeptide highly similar to bacterial ~r-factors. A promoter was identified in the spollGB-spolllG interval by transcriptional fusion to lacZ. It is turned on I hr after the start of ~r ~ synthesis and is specifically activated in the forespore. The tandemly arranged spollGB and spoHIG genes appear to encode homologous proteins that modulate transcription in a sequential fashion during sporulation.

The Baci/lus subtilis spoIlJ locus is defined by a Tn917 insertion which leads to an oligosporogenous phenotype. Here Sporulation of Bacillus subtilis is induced by starvation for either a carbon, a nitrogen, or a phosphorus source. The first recognizable morphological step of this developmental process is the synthesis of an asymmetric septum at one pole of the cell (reviewed in reference 23). This abnormal septation, which segregates the two chromosomes issued from the last round of replication into two unequal compartments, takes place about 60 to 90 min after the end of exponential growth in liquid medium at 37°C. Mutations in the spoIIA and spoIIE operons lead to aberrant structures often characterized by multiple septa, excess membrane synthesis, and deposition of cell wall inside the septa (23). These mutations also block the processing of the inactive precursor of uE, a sigma factor which plays a major role in transcription specificity after the cell has divided into two compartments (35,37). It has been proposed that activation of the spoIIGA product, the presumptive processing enzyme (35), is triggered by the sporulation septum itself, which in turn activates pro_CrE, the spoIIGB product (18,35). Interestingly, the three operons spolIA, spoIIE, and spoIIG are turned on simultaneously about 30 min after the onset of sporulation, and their transcription depends on the products of the spoO genes, suggesting that their expression could be coordinated by a common regulatory mechanism (7,12,16,35).Since some spoO genes are transcribed during exponential growth (4, 40), it can be conjectured that their products respond to the metabolic status of the cell and relay this information by controlling expression of early spo genes, such as some stage II genes. Sequencing of spoOA (9) and spoOF (36) has revealed that their products belong to a family of widespread procaryotic proteins, most of which activate transcription of various regulons in response to specific environmental signals. These proteins are part of a twocomponent system, and their activity is modulated by a second protein acting as a "sensor" and a "transmitter" of some metabolic stimuli (27). It Construction of lacZ fusions. The spoIIA-and spoIIE-lacZ fusions have already been described (35). The spoIIG-lacZ fusion was constructed by subcloning a 518-base-pair (bp)

Lectins are fundamental to plant life and have important roles in cell-to-cell communication; development and defence strategies. At the cell surface; lectins are present both as soluble proteins (LecPs) and as chimeric proteins: lectins are then the extracellular domains of receptor-like kinases (LecRLKs) and receptor-like proteins (LecRLPs). In this review; we first describe the domain architectures of proteins harbouring G-type; L-type; LysM and malectin carbohydrate-binding domains. We then focus on the functions of LecPs; LecRLKs and LecRLPs referring to the biological processes they are involved in and to the ligands they recognize. Together; LecPs; LecRLKs and LecRLPs constitute versatile recognition systems at the cell surface contributing to the detection of symbionts and pathogens; and/or involved in monitoring of the cell wall structure and cell growth.