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A Drosophila RNA polymerase II transcription factor that is specific for at least one of the heat-shock genes has been isolated (designated HSTF for heat-shock transcription factor). This factor is required for active transcription of an hsp 70 gene in addition to RNA polymerase II and another general transcription factor, the A factor. Footprint analysis of the HSTF on the hsp 70 gene reveals that it binds specifically to a 55 bp region upstream from the TATA box. Both coding and noncoding DNA strands are completely protected from DNAase I cleavage by the HSTF . HSTF binding occurs in the apparent absence of RNA polymerase II. The HSTF is present in both heat-shocked and nonshocked cells, although it is more transcriptionally active when isolated from heat-shocked cells. The previously described B factor (an RNA polymerase II transcription factor that binds to the TATA box), isolated from nonshocked cells, is significantly reduced in both binding and transcriptional activity in heat-shocked cells. The potential role of the HSTF and the B factor in the activation of heat-shock gene transcription is discussed.

The jun family of transcriptional activators includes mammalian AP-1 as well as the yeast regulatory protein GCN4. Recently, an additional transcriptional activator has been found in yeast that recognizes the TGACTCA sequence element common in GCN4/AP-1 sites. This factor was designated yAP-1. The structural gene for yAP-1 has now been isolated and characterized. The deduced amino acid sequence predicts a protein of 650 residues, considerably larger than GCN4 or c-Jun. The amino terminus of yAP-1 is homologous to the carboxyterminal DNA-binding domains of GCN4 and e-Jun. Disruption of the YAP1 gene demonstrates this gene is not essential but is required for AP-1 recognition element-dependent transcriptional activation. DNA-affinity blots of proteins from YAP1 cells suggest the presence of additional TGACTCA-binding proteins other than GCN4 and yAP-1. Furthermore, expression of at least one of these related DNA-binding proteins appears to be under control of yAP-1.

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