INTEGRATED MAPPING AND SEQUENCING OF A 115 KB DNA FRAGMENT FROM BACILLUS-SUBTILIS - SEQUENCE-ANALYSIS OF A 21 KB SEGMENT CONTAINING THE SIGL LOCUS

A sequence strategy which combines a low redundancy shotgun approach a nd directed sequencing has been elaborated. Essentially, the sequences , as well as the size of the fragments utilized for a low coverage sho tgun approach, were exploited for the construction of a physical map o f the region to be sequenced. The latter considerably simplified the s ubsequent directed sequencing steps. We report the physical mapping of a 115 kb segment which covers nearly 100 kb of the hisA-cysB region o f the Bacillus subtilis chromosome and contains previously sequenced g enes sigL and sacB. Sequencing and analysis of a 21305 bp segment whic h includes the sigL locus, revealed 21 ORFs, apparently belonging to a t least seven transcription units. This segment has a G + C content gr eater than 47%, compared to 43% characteristic of the flanking regions , and mainly consists of genes whose products seem to be involved in t he synthesis of an exopolysaccharide. These observations leave open th e possibility that the analysed fragment has been acquired through hor izontal transfer.