Biomedical subjects

A Wildeman

Publications and source records attributed to A Wildeman.

5 recordsLinked to original sources

PubMed1986

Multiple sequence motifs are involved in SV40 enhancer function.

A systematic mutagenesis of the SV40 enhancer indicates that it spans approximately 100 bp and is composed of at least two distinct DNA domains which exhibit very little enhancing activity on their own. Their association results in a 400-fold enhancement of transcription, virtually irrespective of their relative orientation and, to some extent, of the distance between them. Enhancer activity can also be generated by duplication of either domain. We show also that the activity of each domain is due to the presence of several specific sequence motifs. These motifs are found assorted in different combinations in other viral and cellular enhancers.

Base Composition↗

PubMed1985

All six GC-motifs of the SV40 early upstream element contribute to promoter activity in vivo and in vitro.

Recombinants in which the six GC-motifs (I-VI) present in the upstream element of the SV40 early promoter region have been point mutated either individually or in pairs were used to determine the possible contribution of each GC-motif to the function of the overlapping early-early and late-early SV40 promoters. GC-motif I, and to a lesser extent, GC-motifs II and III, are critical for initiation at the early-early start sites. GC-motifs IV-VI play a subsidiary role. Mutations in GC-motifs I and II do not decrease the activity of the late-early promoter, whereas mutations in the GC-motifs III-VI have a moderate effect on it. The in vivo phenotype of the GC-motif mutants can be almost fully reproduced in vitro using a nuclear extract. DNase I protection footprinting experiments using wild-type or mutated templates and nuclear extracts indicate that each GC-motif behaves principally as an independent protein-binding site, presumably for transcription factor Sp1. The effect of changing the position of the 21-bp repeat region on initiation from the early-early and late-early start sites indicates that there is little flexibility in the position in which this upstream element can efficiently activate initiation of transcription from these start sites.

Base Sequence↗

PubMedDate not supplied

A trans-acting factor is responsible for the simian virus 40 enhancer activity in vitro.

Stimulation of in vitro transcription by the simian virus 40 enhancer involves a rapid and stable binding of a trans-acting factor with both the 5'- and 3'-domains of the enhancer sequence. The enhancer factor, which differs from other types of transcriptional factors, can interact with other enhancer elements.

Adenoviridae↗

PubMedDate not supplied

Requirement of stereospecific alignments for initiation from the simian virus 40 early promoter.

The distance between the simian virus 40 early promoter elements has been altered by inserting either odd or even multiples of half a DNA turn. There are marked differences in the in vivo effects of these two types of insertions on initiation of transcription from this promoter.

Base Sequence↗

PubMedDate not supplied

Cell-type specific protein binding to the enhancer of simian virus 40 in nuclear extracts.

Enhancers are cis-acting activators of transcription from homologous or heterologous promoter elements of viral and cellular genes (see refs 1-6 for reviews). The activity of the simian virus 40 (SV40) (refs 7-9) and immunoglobulin heavy-chain gene (IgH) (refs 10, 11) enhancers has been reproduced to some extent in vitro and appears to be mediated by trans-acting factors both in vitro and in vivo. The SV40 enhancer consists of multiple sequence motifs in two domains, A and B (Fig. 1, see ref. 14): domain B contains GT-I and -II and two TC motifs, of which only TC-II is important for enhancer activity in HeLa cells; and domain A contains the P and the two Sph motifs, the repetition of which generates the sequence 5'-ATGCAAAG-3', similar to the 'octameric' sequence of the IgH enhancer, (Fig. 4i; refs 14, 16), where it is important for enhancing activity. Each SV40 enhancer motif is a binding site for a protein or proteins present in HeLa cell nuclear extracts. Unlike the SV40 enhancer, which is active in HeLa and lymphoid B cells, the IgH enhancer is preferentially active in B cells, suggesting that not all the trans-acting factors necessary for its activity are present in HeLa cells. However, the IgH enhancer can compete with the SV40 enhancer in vitro in HeLa or lymphoid cell extracts and in vivo in B cells. Here we show that both human HeLa and BJA-B lymphoid B-cell nuclear extracts contain proteins that bind to specific, sometimes overlapping, motifs of the SV40 enhancer. Some binding is cell-specific, suggesting that it is not the same set of sequence motifs and proteins that is responsible for the enhancer activity in the two cell types. This is confirmed by our results obtained in vivo with mutated SV40 enhancers.

B-Lymphocytes↗