Multiple Point Mutations Affecting the Simian Virus 40 Enhancer

Abstract

Enhancers, or activators, dramatically increase the transcriptional activity of certain eukaryotic genes. A series of multiple point mutations affecting the simian virus 40 (SV40) enhancer-activator region were generated in order to define the nucleotide sequence required for this function. Three independent assays provided information leading to the identification of nucleotides essential for enhancer function. One class leads to a decrease in gene expression, while the second completely abolishes functional activity. One critical replacement appears to be the first G (guanine) in a sequence TGGAAAG (T, thymine, A, adenine) located in the 5' region of the 72 base-pair repeat of SV40. Comparison of this sequence with nucleotide sequences in other known enhancers leads to the identification of potential related core elements.

Multiple sequence motifs are involved in SV40 enhancer function.

“…Although there are no strong overall sequence homologies between different enhancers, several short and degenerate consensus sequences have been identified, but their functional significance has been studied only in a limited number of cases. On the basis of sequence homology between various enhancers and the results of a random mutagenesis, Weiher et al (1983) Figure 2) appears particularly important. Mutations of the other residues of this sequence element seem better tolerated in GT-motif I than in GT-motif II.…”

“…Although different enhancers do not share extensive sequence homologies, short and degenerate consensus sequences have been pointed out Weiher et al, 1983; Hen et al, 1983; Nordheim and Rich,…”

Activation of a translocated human c-myc gene by an enhancer in the immunoglobulin heavy-chain locus

“…The nucleotide sequence of a portion of the J H -C μ region of the human germ-line clone pH18-CL-10 was determined and compared with that of the corresponding region of mouse DNA ( Figure 5), which contains the enhancer core sequences 30 which are common to enhancers so far defined. Core-like sequences are present in the human DNA: there is a 67% matching between the 140 bp of mouse DNA that contains most, if not all, of the murine enhancing activity and the corresponding human sequence.…”

Xrep, a plasmid-stimulating X chromosomal sequence bearing similarities to the BK virus replication origin and viral enhancers

“…7b). Core sequence #1 is nearly identical to the core sequence first described in SV40 (35,36). Core sequences 2-5 are identical to the Ela homology or core sequence (11,12,28) except that #2 is on the complementary strand.…”