The expression of Bacillus subtilis $alpha$-amylase from the phoA-amyE fusion gene in recombinant E. coli was investigated under various environmental conditions. The overexpression of cloned $alpha$-amylase caused retardations in cell growth and synthesis of alkaline phosphatase (AP) from the chromosomal phoA gene. The change of culture temperature from $37^circ{C}$ to $30^circ{C}$ increased the specific activities of both $alpha$-amylase and $eta$-lactamase by six and two times, respectively, whereas the AP activity remained unchanged. The experiments with chlorampenicol (a translation inhibitor) suggested the enhancement of $alpha$-amylase activity at $30^circ{C}$, and this was partly due to the stability of $alpha$-amylase itself. The further decrease of the temperature to $25^circ{C}$ slowed down both the cell growth and cloned-gene expression rate. The $alpha$-amylase activity showed a maximum at pH of 7.4 while alkaline phosphatase was most effectively produced at pH of 8.3.