All vectors use the strong promoter preceding the groESL operon of Bacillus subtilis fused to the lac operator allowing their induction by addition of IPTG. While the background level of expression of these expression cassettes is very low in the absence of the inducer, an induction factor of about 1,300 was measured using the bgaB reporter gene. The amount of recombinant protein produced after addition of IPTG may represent 10 and 13%, respectively, of the total cellular protein. High level secretion of amyQ α-amylase and cellulase A and B of Clostridium thermocellum was demonstrated. An efficient Shine-Dalgarno sequence as well as a multiple cloning site (BamH I, Xba I, AatII, SmaI) were also inserted. To obtain secretion of recombinant proteins, the coding region for the signal peptide of the amyQ gene encoding an α-amylase was fused to the SD sequence of pHT01, thereby constructing pHT43.