Ty-mediated gene expression of th( Saccharomyces cerevisiae is control) (insertions/suppressors/transposons)

Five Ty insertion mutations were isolated at the LYS2 locus of Saccharomyces cerevisiae. Genetic and phys- ical analyses show that four Ty insertions are in the 5' noncod- ing region of LYS2 and one is within the structural gene. Three of these Ty elements have been cloned and characterized. The Ty mutations differ from each other in restriction pattern, phenotypic effects on LYS2, reversion frequency, and the na- ture of reversion events. Spt2 and spt3 mutations, known to suppress Ty insertions and their solo 8 derivatives at HIS4, can also suppress at least one of the Ty insertions (Ty61) at LYS2 and can also suppress the Lys- phenotype of a solo 8 derivative of another Ty insertion (Ty128) at LYS2. These re- sults demonstrate that spt mutations can suppress Ty and 6 mutations at both HIS4 and LYS2, suggesting that they are general for their effects on Ty and 8 elements. Transposable (Ty) elements of Saccharomyces cerevisiae are repeated elements about 6 kilobase pairs (kb) in length that have direct repeats of about 300 base pairs (bp) at their ends (8 sequences) (1). Standard S. cerevisiae strains have about 35 Ty elements occurring naturally in the haploid genome (1). Considerable homology exists between different Tys, even though most elements have a unique restriction map. Solo 8 sequences, unassociated with the complete Ty element, are present in about 100 copies in the genome (1). These 8 sequences are thought to arise by recombination be- tween the 8 repeats of intact Ty elements. 8-8 recombina- tion has been documented for Ty elements inserted at HIS4 (2) and at ADH2 (3). Several mutations in S. cerevisiae result from alteration in expression of a gene by the insertion of a Ty element in the regulatory region of that gene (4). Such insertion mutations generally result in one of two opposite effects-inhibition of gene expression or constitutive high-level gene expression. The phenotypes of Ty insertion mutations can be affected by unlinked genes. For example, many Ty insertions that result in constitutive gene expression are under control of the mat- ing type locus of the cell (5-7). Recently, mutations have been characterized in seven genes (SPT genes) that suppress the His- phenotype of some Ty insertions and their solo 8 derivatives in the 5' noncoding region of the HIS4 gene (8). In this paper we report on the isolation and characteriza- tion of Ty insertions at the L YS2 locus. We have found that spt2 and spt3 mutations can suppress the Lys- phenotype of Ty and 8 insertions at L YS2, suggesting that suppression by spt mutations is not specific to the HIS4 gene.