ROLE OF A SMALL RNA POL-II SUBUNIT IN TATA TO TRANSCRIPTION START SITE SPACING

The yeast shi mutation affects the spacing between the TATA promoter e lement and transcription initiation sites; for the H2B and ADH1 genes, a series of start sites located similar to 50 - 80 bp downstream of T ATA is used in addition to the wild-type initiation sites located at a round 100 bp from TATA (1). Here, the yeast SHI wildtype gene has been isolated by complementation and shown to be identical to RPB9, the ge ne encoding a small subunit of RNA polymerase II. A point mutation in the shi gene, changing a cysteine residue in a putative zinc ribbon mo tif into a phenylalanine residue, was demonstrated to permit the obser ved usage of upstream initiation sites. Deletion of the non-essential SHI gene also results in usage of upstream initiation sites and causes conditional growth defects.