The recA gene of Proteus mirubilk (recApm) has been cloned into the Pat1 site of the Bacillus promoter-probe plasmid pPL603. When present on this plasmid, the rectlpm') gene is expressed in B. subtilie under the control of its own transcriptional and translational signals. It is concluded that the high AT-content of the DNA sequence upstream of the -35 region is of decisive importance for the usage of the recApm promoter by the B. subtilis RNA polymerase. The results are discussed in relation t o the expression barriers found to exist for genes from gram-negative bacteria in the gram-positive B. subtilia.
The gram-positive bacterium Bacillus subtilis is restricted in its ability t o express genes of the gram-negative bacterium Escherichia coli while genes of B. suhtilis become quite well expressed after introduction into E. coli (EHI.~LJCK 1978, KRIWT et al. 1978). So far, only the tetracycline resistance gene of the E . coli plasmid pSR322 has been reported t o become naturally expressed in B. subtiZis (KREFT et al. 1983). On the other hand, there is in B. subtilis, with few exceptions (WESTPIIZLING et al.
1985), no barrier to the expression of genes from gram-positive bacteria (STALLCUP et at. 1976, MCLAUGH-LIN et al. l98lb). The barriers for expression of E. coli genes in B. subtilis are due to differences in transcription and translatiori of the two species. These differences are, however, not fully understood (see for review: LIZDEMA" 1983, nor 1984). In contrast t o E. coli, transcription in B. subtilis is regulated by a cascade of RNA polymerases. The promoter specificity of which is determined by distinct sigma-cofactors l ) Abbreviations: UV ultraviolet, Cm resistance t o chloramphenicol, Km resistance to kanamycin, SDS sodium dodecyl sulfate, kb kilobases, bp base pairs, pPL608recApz the arrow abovc recApm indicates the orientation of the gene insert 5*