New systems for producing recombinant proteins

A recombinant vector for heterologous expression of a recombinant protein in a Streptomyces host cell bearing an expression cassette comprising:

• a promoter, a regulatory element, and a polynucleotide encoding a recombinant protein operably linked to said promoter and regulatory element;
• wherein:
• said promoter is an engineered kasO promoter (kasOp*) having sequence SEQ ID NO:
• 10;
• said regulatory element is an optimized synthetic SR40 ribosome-binding site (RBS) having sequence SEQ ID NO:
• 11;
• the polynucleotide encoding for the recombinant protein of interest encodes for a recombinant protein that includes a N-terminal signal peptide;
• and
• the recombinant vector is a single-site integrating vector.