A Transcriptional Analysis of the Human c-Ha-ras1 Oncogene

The pattern of transcription initiation for the human c-Ha-rasl gene has been investigated using several experimental methods. These analyses demonstrated multiple clusters of transcription initiation sites distributed over an approximately 200 bp non-coding, upstream exon (termed exon -1), which is separated from the ATG codon by an 1040 bp intron. Mutational analysis of the promoter region identified a short positive regulatory element, located between positions -243 to -196, relative to the donor splice site of exon -1. This element contains known regulatory sequence motifs. Furthermore, a putative negative regulatory element, with an unusual DNA sequence, was identified between positions -103 to -34, relative to the same donor splice site. It has also been demonstrated that the human c-Ha-rasl promoter region can function bidirectionally. The sequence directing the "reverse-orientation" promoter activity was located to between positions, -392 to -196, relative to the exon -1 donor splice site of the c-Ha-rasl gene. Transcription of the c-Ha-rasl gene was shown to be increased approximately 20 fold when covalently linked to the SV40 enhancer element. This result is the first direct demonstration that the SV40 enhancer can increase transcription of "housekeeping-type" genes and this result also has important implications for the possible methods of oncogenic activation of this gene. The 1040 bp intron located between exon -1 and the first coding exon (exon 1) was found to contain sequences within its 5' end, which were moderately repetitive within the human and mouse genomes, and homologous to abundantly transcribed, non-polyadenylated RNAs from various human cell lines. However, the functional significance, if any, of this result is unclear