Fusion of Escherichia coli lacZ to the cytochrome c gene of Saccharomyces cerevisiae.

Hybrid genes between the Escherichia coli lacZ gene and the iso-1-cytochrome c (CYC1) gene of Saccharomyces cerevisiae were constructed by recombination in vitro. Each of the hybrid genes encodes a chimeric protein with a cytochrome c moiety at the amino terminus and an active beta-galactosidase (beta-D-galactoside galactohydrolase, EC 3.2.1.23) moiety at the carboxy terminus. When these hybrids are introduced into S. cerevisiae on plasmid vectors, they direct synthesis of beta-galactosidase. beta-Galactosidase levels directed by one such plasmid display the pattern of regulation normally seen for cytochrome c (i.e., a reduction of synthesis in cells grown in glucose). This plasmid contains one codon of CYC1 fused to lacZ, and the fused gene is preceded by the 1100 nucleotides that lie upstream from CYC1. An analysis of deletions in the upstream DNA suggests that sequences required for efficient transcription initiation of CYC1 lie within the DNA segment 250--700 base pairs upstream from the start of the CYC1 coding sequence. This region is at least 130 base pairs upstream from the "Hogness box" sequence that precedes the CYC1 coding sequence.