COMPARATIVE MUTATIONAL ANALYSIS OF WILD-TYPE AND STRETCHED TRANSFER RNA-3-LEU GENE PROMOTERS

We demonstrate that, when the yeast tRNA3Leu gene is stretched so that the distance between the two portions of the intragenic promoter is increased to 365 base pairs, the A and b blocks remain functional. Mutations in the A block, which show a weak phenotype when inserted in the wild type, exert a dramatic effect when inserted into the stretched gene. Experiments with extensively purified transcription factor .tau. indicate that the .tau.B-B block interaction is not influenced by A-B distance; only the ability of .tau.A to interact with A block sequences is affected, possibly because of the additional free-energy cost of forming a large loop of the intervening DNA.