THE PCSA GENE IS IDENTICAL TO DIND IN ESCHERICHIA-COLI

The pcsA68 mutant of Escherichia coil is a cold-sensitive mutant which forms long filaments with a large nucleoid in the central region at 2 0 degrees C. We here show that (i) the coding region for the pcsA gene is identical with orfY located upstream of pyrE and can be deleted wi thout loss of viability; (ii) pcsA is also identical to dinD, a DNA da mage-inducible gene, whose expression is regulated by the LexA-RecA sy stem; (iii) the cold-sensitive phenotype of the pcsA68 mutation is sup pressed by triangle recA or lexA1 (Ind(-)) mutation, but not by sulA i nactivation; (iv) overproduction of PcsA68 leads to inhibition of cell growth in recA(+) and triangle recA strains at 20 and 37 degrees C, b ut PcsA(+) does not show such an effect at any temperature; (v) SOS re sponse is induced in the pcsA68 mutant cells at 20 degrees C. We discu ss the possible function of the pcsA gene, comparing it with the sulA or the dif-xerCD function, We also describe a new method for gene disr uption with positive and negative selection.