INVITRO BINDING TO THE LEUCINE TRANSFER-RNA GENE IDENTIFIES A NOVEL YEAST HOMEOBOX GENE

In a search for gene products of Saccharomyces cerevisiae interacting with the internal promoter of yeast tRNA genes two genes encoding a homeodomain protein of the Drosophila Antennapedia type were isolated. One of them codes for Pho2, and the second codes for a previously unknown protein (Yox1). The corresponding gene, termed YOX1, maps to chromosome 16. The amino acid sequence of Yox1 shows a remarkable similarity within the homeobox domain to many proteins from a wide variety of sources. Fusion proteins that contain sequences encoded by these genes demonstrate that the genes encode DNA-binding proteins that are capable of binding to the DNA of the leucine tRNA gene in vitro. However, deletion of YOX1 gene activity does not give rise to a scorable mutant phenotype. This result leaves open whether Yox1 binding to the leucine tRNA gene is necessary for the in vivo regulation of the gene and its suggests that the YOX1 gene codes for a nonessential product.