The structural gene, pen, for the beta-lactamase of B. licheniformis has been cloned into a lambda vector and shown to be expressed at a low rate in E. coli. The cloned pen gene appears to be expressed from a promoter within the fragment of B. licheniformia DNA, since its rate of expression is not affected by the presence of the phage repressor, the absence of the phage's positive-control functions, or the position or orientation of the gene within the phage genome.