Functional analysis of the fic gene involved in regulation of cell division

We have shown that cAMP may be a regulation factor in cell division of Escherichia coli (Utsumi et al., 1982, 1989). The fic (filamentation induced by cAMP) gene of this system found previously (Utsumi, et al., 1982) was analysed in this study. The open reading frame of the fic gene coded for 200 amino acids. The pabA (p-aminobenzoate synthase) gene was found downstream from the fic gene. The distance between the end of fic and the start of pabA was 31 base pairs. To deduce the function of Fic protein, the fic gene was destroyed by the kanamycin-resistant (Kmr) gene and the fic gene was shown to be essential for growth of E. coli. Such mutants required PAB (p-aminobenzoate) or folate for growth. These data suggested that the Fic protein is involved in the synthesis of PAB or folate and the fic gene could be part of a pab operon. In cells starved of them, cell division was inhibited. Addition of folate also repressed the filamentation induced by cAMP at 43 degrees C in the fic-1 mutant. These results would indicate that Fic protein and cAMP are involved in a new regulatory mechanism of cell division via folate metabolism. Furthermore, it is also shown that cell division could be controlled by coordination of cAMP, Fic and Fts proteins.

Control mechanism of the Escherichia coli K-12 cell cycle is triggered by the cyclic AMP-cyclic AMP receptor protein complex

The role of cyclic AMP (cAMP) in the cell cycle of Escherichia coli K-12 was studied in three mutant strains. One was KI1812, in which the cya promoter is replaced by the lacUV5 promoter. In KI1812, isopropyl-beta-D-thiogalactopyranoside induced the synthesis of cya mRNA, and at the same time cell division was inhibited and short filaments containing multiple nuclei were formed. The other strains were constructed as double mutants (NC6707 cya sulB [ftsZ(Ts)] and TR3318 crp sulB [ftsZ(Ts)]). In both double mutants, filamentation was repressed at 42 degrees C, but it was induced again by addition of cAMP in strain NC6707 and introduction of pHA7 containing wild-type crp in TR3318. These results indicate that lateral wall synthesis in the E. coli cell cycle is triggered by the cAMP-cAMP receptor protein complex.

Cloning of the fic-1 gene involved in cell filamentation induced by cyclic AMP and construction of a delta fic Escherichia coli strain

PA3092 is an Escherichia coli mutant that forms filaments at 43 degrees C in the presence of cyclic AMP (cAMP). The mutation responsible for this phenotype is called fic-1. We cloned fic-1 from PA3092 by selection for the neighboring argD gene. The fic-1 gene product had a relative molecular mass of 21 kilodaltons by the maxicell method. A strain with the fic gene completely deleted was constructed by replacing fic with a kanamycin resistance gene. In one of the fic-deleted strains derived from PA3092, cAMP did not induce cell filamentation at 43 degrees C, but it did in the same strain harboring a plasmid containing the fic-1 gene. These results indicate that the fic-1 gene product is necessary for the induction of cell filamentation by cAMP but is dispensable to the cell. We also found that high levels of NaCl suppressed the cell filamentation induced by cAMP.

Expression of the adenylate cyclase gene during cell elongation in Escherichia coli K-12

Expression of the adenylate cyclase gene (cya) in synchronized Escherichia coli cells was investigated by using the cya-lacZ protein and operon fusion plasmids. The regulation of cya expression during the cell cycle is characterized as follows: cya is expressed during cell elongation; expression is repressed during cell division; regulation is exerted at the transcriptional level. To test cya expression during cell elongation, we constructed a plasmid (pLCR1) in which the lacUV5 promoter operator was fused to the structural gene of cya and investigated the effect of cya expression by isopropyl-beta-D-thiogalactopyranoside (IPTG) on the cell division of cells containing pLCR1. By the addition of IPTG, cell division was inhibited and filaments were formed. Such an inhibitory effect was antagonized by adding cyclic GMP to the culture medium and was not observed in the crp mutant.