ROLLING-CIRCLE PLASMIDS FROM BACILLUS-SUBTILIS - COMPLETE NUCLEOTIDE-SEQUENCES AND ANALYSES OF GENES OF PTA1015, PTA1040, PTA1050 AND PTA1060, AND COMPARISONS WITH RELATED PLASMIDS FROM GRAM-POSITIVE BACTERIA

Most small plasmids of Gram-positive bacteria use the rolling-circle m echanism of replication and several of these have been studied in cons iderable detail at the DNA level and for the function of their genes. Although most of the common laboratory Bacillus subtilis 168 strains d o not contain plasmids, several industrial strains and natural soil is olates do contain rolling-circle replicating (RCR) plasmids. So far, k nowledge about these plasmids was mainly limited to: (i) a classificat ion into seven groups, based on size and restriction patterns; and (ii ) DNA sequences of the replication region of a limited number of them. To increase the knowledge, also with respect to other functions speci fied by these plasmids, we have determined the complete DNA sequence o f four plasmids, representing different groups, and performed computer -assisted and experimental analyses on the possible function of their genes. The plasmids analyzed are pTA1015 (5.8 kbp), pTA1040 (7.8 kbp), pTA1050 (8.4 kbp), and pTA1060 (8.7 kbp). These plasmids have a struc tural organization similar to most other known RCR plasmids. They cont ain highly related replication functions, both for leading and lagging strand synthesis. pTA1015 and pTA1060 contain a mobilization gene ena bling their conjugative transfer. Strikingly, in addition to the conse rved replication modules, these plasmids contain unique module(s) with genes which are not present on known RCR plasmids of other Gram-posit ive bacteria. Examples are genes encoding a type I signal peptidase an d genes encoding proteins belonging to the family of response regulato r aspartate phosphatases. The latter are likely to be involved in the regulation of post-exponential phase processes. The presence of these modules on plasmids may reflect an adaptation to the special condition s to which the host cells were exposed. (C) 1998 Federation of Europea n Microbiological Societies. Published by Elsevier Science B.V.