Expression of a chromosomal gene for human leucocyte interferon A was obtained due to interaction of 5'-nontranslating region of a cloned interferon gene with the regulatory sequences from UNA3 yeast gene. The sequence of 5'-nontranslating region from interferon gene essential for its expression in yeast is localized within 130 b p. from the initiating codon. Due to increasing of plasmid stability and copy number a 60-fold increase. in interferon yield was obtained in yeast transformants reaching the level of 6 X 10(7) u X 1(-1). The data are presented supposing the existence of functional polycistronic mRNA in yeast.