Abstract: Methods are described for the production of the .beta.-subunit of reverse transcriptase using recombinant DNA techniques. Methods and compositions are described for cloning and expressing the gene coding for the .beta.-subunit of reverse transcriptase and characterizing and isolating the gene product. The recombinant plasmids constructed herein contain the necessary signals and controls for efficient expression of the reverse transcriptase gene in bacteria and other microorganisms. The isolated reverse transcriptase gene product is a functional, metabolically stable and biologically active protein.

Abstract: DNA cloning and expression vectors capable of replication in a microbial host comprising from upstream to downstream (a) at least one promoter; (b) a translation start codon; (c) a cloning segment which provides a means for inserting nucleic acid sequences and (d) a sequence coding for a detectable gene product, out of translational phase with the translation start codon but capable of being readjusted to the translational phase of said start codon by insertion into the cloning segment of nucleic acid sequences containing the proper number of nucleotides for readjustment, said gene product providing a means for detecting expression of inserted nucleic acid sequences.