We previously isolated the AML1 gene, which is rearranged by the t(8;21) translocation in acute myeloid leukemia. The AML1 gene is highly homologous to the Drosophila segmentation gene runt and the mouse transcription factor PEBP2 alpha subunit gene. This region of homology, called the Runt domain, is responsible for DNA-binding and protein--protein interaction. In this study, we isolated and characterized various forms of AML1 cDNAs which reflect a complex pattern of mRNA species. Analysis of these cDNAs has led to the identification of two distinct AML1 proteins, designated AML1b (453 amino acids) and AML1c (480 amino acids), which differ markedly from the previously reported AML1a (250 amino acids) with regard to their C-terminal regions, although all three contain the Runt domain. The large C-terminal region common to AML1b and AML1c is suggested to be a transcriptional activation domain. AML1c differs from AML1b by only 32 amino acids in the N-terminal. Characterization of the genomic structure revealed that the AML1 gene consists of nine exons and spans > 150 kb of genomic DNA. Northern blot analysis demonstrated the presence of six major transcripts, encoding AML1b or AML1c, which can all be explained by the existence of two promoters, alternative splicing and differential usage of three polyadenylation sites. A minor transcript encoding AML1a which results from alternative splicing of a separate exon can be detected only by reverse transcription-polymerase chain reaction amplification. The distinct proteins encoded by the AML1 gene may have different functions, which could contribute to regulating cell growth and/or differentiation through transcriptional regulation of a specific subset of target genes.

HPV16 DNA is often integrated in cancers, disrupting the E1 or E2 genes. E2 can repress the E6/E7 promoter, but other models have been proposed to explain why integration promotes malignant progression. E1 and E2 are required for viral replication, and so genetic analysis of their role in transcriptional regulation is complex. Therefore, we developed an extrachromosomal vector containing HPV16 to undertake a genetic analysis of the E1 and E2 genes. We demonstrate that the E2 protein is primarily a transcriptional repressor when expressed from the virus. Furthermore, repression requires both the transactivation function of E2 and specific binding of E2 to the LCR. We find no evidence that the E1 protein directly modulates HPV16 gene expression. However, certain E1 mutations modulated transcription indirectly by altering splicing of E2 mRNA species. These data provide important insight into which E1 and E2 functions are optimal targets for anti-viral therapies.

The mechanism of transcriptional regulation of the H‐2Kbm1 major histocompatibility complex (MHC) class I gene by adenovirus type 12 E1A (Ad12‐E1A) was studied in transfected rat embryonal fibroblasts. Results of long‐term expression of the chloramphenicol acetyl transferase (CAT) gene placed under the control of the 5′‐flanking region of the mouse MHC class I gene. H‐2Kbm1, and the results of nuclear run‐on transcription assays, yield evidence for both positive and negative regulation of H‐2Kbm1 by E1A gene product. Deletion studies in the H‐2Kbm1 promoter region revealed that a proximal 58 bp upstream sequence (‐194 to ‐136, relative to the cap site) and a distal 316 bp sequence (‐1837 to ‐1521) respectively contribute to positive and negative regulation mediated by the E1A gene product. Both regulatory elements of MHC class I gene promoter region are responsible for the differential expression of the H‐2Kbm1 gene in Ad12 transformed cells. A nuclear factor binding to the negative element has been detected only in extracts derived from cells expressing Ad12‐E1A.