Interaction of CAP sequence site binding factor and transcription factor IID preceding and following binding to the adenovirus 2 major late promoter

Defective binding of IRFs to the initiator element of interleukin-1beta-converting enzyme (ICE) promoter in an interferon-resistant Daudi subline

To investigate mechanisms of interferon (IFN) resistance, we have established an IFN-resistant Daudi subline (Daudi(res)), which is 1 X 10(4) times more resistant to IFN-alpha than parental cells. Among the IFN-inducible genes examined, only ICE mRNA expression was deficient in Daudi(res) cells. We then analyzed the regulatory mechanisms of ICE transcription, and found that IFN-induced activation of the ICE promoter was dependent on the binding of IRFs to its initiator (Inr) element. Inr binding of IRFs was markedly diminished in Daudi(res) cells, and forced expression of IRF-1 was able to activate the ICE promoter to the level of parental cells. These results suggest that IRFs and their target genes, as represented by ICE in this study, are involved in IFN resistance.

Expression of the carboxypeptidase E gene: characterization of the initiator-binding proteins

Several of the genes for enzymes involved in peptide hormone processing, such as carboxypeptidase E (CPE), do not contain a TATA box. The region surrounding the major transcription initiation site of the CPE gene has sequence homology with the 'initiator' (Inr) elements of the TATA-less terminal deoxynucleotidyltransferase (TdT) gene, and the adenovirus major late (AdML) and other promoters. To investigate the promoter region of the CPE gene, GH4C1 cells were transiently transfected with constructs containing the luciferase reporter gene attached to various portions of the rat CPE gene (-395 to +45). Positive regulator elements were detected in positions -84 to -12 and +30 to +47. However, the Inr-like element of the CPE gene (-12 to +20) produced detectable luciferase activity in the absence of upstream and downstream sequences. This region of the CPE gene was much more active when expressed in the normal (sense) orientation than when expressed in the antisense orientation. A mutation within the consensus sequence between CPE and other Inr elements was much less active than the wild-type sequence. Interestingly, deletion of the Inr and surrounding sequences produced a large increase in the transcription from upstream sites, suggesting that proteins which bind at, or near, the Inr sequence suppress transcription from other sites. To characterize GH4C1 nuclear proteins which bind to the CPE gene, Southwestern blotting, UV cross-linking, and gel shift analyses were performed. The Southwestern analysis showed that the CPE and AdML Inr sequences labeled several proteins of similar sizes which are distinct from the transcription factor USF; this factor has been previously reported to bind to the AdML Inr sequence. A CPE Inr-binding protein co-purifies with an AdML Inr-binding protein on a CPE Inr affinity column. Gel shift assays showed that with some binding conditions, the proteins that bind to the CPE sequence also bind to the TdT and AdML Inr elements. Taken together, these results indicate that the -12 to +20 region of the CPE gene has the properties of an Inr element which binds some, but not all, of the factors which bind to other Inr elements.

The arthropod initiator: the capsite consensus plays an important role in transcription

Approximately 25% of arthropod RNA polymerase II-transcribed promoters contain one or more copies of the sequence TCAGT beginning within the interval (-10, +10). The clear statistical overrepresentation of this sequence and, to a lesser extent, of its cognates ACAGT, GCAGT, and TCATT, implies that they may be significant promoter elements. Their collective sequence similarity to vertebrate initiators (Inrs) of the TdT class suggests that the vertebrate and arthropod elements are homologous. Prior work in vertebrate systems has emphasized the role of the Inr in promoters lacking TATA boxes, where it can serve as an alternate staging site for polymerase II initiation. However, it is clear that the Inr sequence is by no means restricted to TATA-deficient promoters. Functional tests using the TATA-containing Drosophila gene Eip28/29 support the idea that the Inr is a facultative promoter element, required for efficient transcription under some conditions. For example, the Inr protects basal expression of Eip28/29 from the silencing effect of ecdysone response elements. In addition, the Inr is required for the function of an enhancer of basal activity in Eip28/29. We conclude that Inrs are promoter elements found sporadically throughout the higher eukaryotes, that the requirement for an Inr depends upon the array of other promoter elements which may be present in a given gene, and that Inrs may permit enhancers to discriminate among promoters.