The expression of human leucocyte interferon alpha F gene in plasmid pLM-IFN alpha F-273 is controlled by a hybrid tac (trp-lac) promoter. A structural gene for interferon alpha F is a component of the hybrid operon lacZ'-IFN alpha F-TcR, that contains an E. coli trp-operon intercystronic region. Plasmid pLM IFN alpha F-273--directed interferon synthesis allows to obtain about 10(7) IU/l. This plasmid was cloned in broad-host-range vector plasmid pAYC31. The hybrid bi-repliconed plasmid containing interferon gene as well as its single-repliconed deletion derivatives obtained by the in vivo recombination, were introduced into obligate methylotroph Methylobacillus flagellatum KT and Pseudomonas putida PpG6. Methylotrophic strain and Pseudomonas were able to transcribe the interferon gene from E. coli tac promoter, the yield of interferon being 2-4-fold higher as compared with the one in the initial host.