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G C Das

Publications and source records attributed to G C Das.

At least 37 records · Page 2Linked to original sources
PubMed1986

The chicken delta 1-crystallin gene promoter: binding of transcription factor(s) to the upstream G+C-rich region is necessary for promoter function in vitro.

There are two linked delta-crystallin genes in the chicken (5' delta 1-delta 2 3'). Only the delta 1 gene has been shown definitively to be active in the lens. Transcription of deletion mutants, reported here, shows that the sequences necessary for the functioning of the delta 1 promoter in a HeLa cell extract are located upstream from the RNA initiation site, between nucleotide positions -121 and -38. This region includes a number of G+C-rich motifs, including one hexanucleotide sequence, CCGCCC, that is repeated six times in the simian virus 40 (SV40) promoter. Competition experiments with purified fragments from the delta 1-crystallin gene promoter showed that binding of transcription factor(s) from the HeLa cell extract to this G+C-rich region is required for promoter activity in vitro. Further, competition experiments using three different fragments from the SV40 promoter suggest that the transcription factor(s) is similar to Sp1, which stimulates transcription by binding to the G+C-rich 21-base-pair repeats of the SV40 promoter, and differs from that which interacts with the SV40 enhancer region.

Animals↗
PubMed1985

Simian virus 40 early promoter mutations that affect promoter function and autoregulation by large T antigen.

A set of nine mutants containing point mutations, and small deletions or insertions, were constructed in the early promoter region of simian virus 40 (SV40) to determine the role of the DNA sequences between the TATA box and the six upstream G + C-rich clusters in early transcription. The mutant templates were tested for transcription activity in vitro in HeLa cell extracts and in vivo in CV-1 and COS cells using the chloramphenicol acetyl transferase gene (CAT) assay. Both in vitro and in vivo results show that the narrow region from nucleotide positions 38 to 41 is an important domain of the early promoter. Deletion and insertion mutations most strongly affect the level of transcription. Specifically a four base-pair deletion in the promoter region enhances the level of transcription four- to sixfold in vitro, but causes a fourfold suppression of CAT gene expression in the in vivo assay. These opposite effects may result from changes in spacing under in vitro and in vivo conditions between the TATA box and the G + C-rich motifs where transcription factors may make simultaneous contact. Of the three T antigen binding sites (I, II and III), sites I and II have already been shown to be involved in the autoregulation of early transcription. Our mutational analyses demonstrate the role of site III, which partially overlaps with nucleotide positions 38 to 41, in the autoregulation of the SV40 early promoter.

Antigens, Viral, Tumor↗
PubMed1979

Ethidium bromide binding to core particle: comparison with native chromatin.

Ethidium bromide intercalation into DNA of nuclease digested erythrocyte chromatin and core particle, was followed at low ionic strength by fluorescence measurements, equilibrium dialysis using 14C labelled dye, circular dichroism and electron microscopy. High affinity binding sites in the chromatin are no more present in the core particle, i.e. when the linker is removed. In the case of core particle, a cooperative process occurs, accompanied by a partial stripping of the DNA from the core histone. Finally two populations of core particles can be detected by electron microscopy as far as their binding properties are concerned.

Animals↗
PubMed1978

Superstructure and CD spectrum as probes of chromatin integrity.

Two types of chromatin were extracted from the same stock of rat liver nuclei by a short exposure to micrococcal nuclease and by shearing respectively. These two materials which are identical in their protein/DNA content and by the presence of the five histones, were compared by means of circular dichroism and electron microscopy. Under the electron microscope and in absence of any divalent cation a superstructure of the unfixed chromatin fiber can be viewed only with native material but is no more present in sheared one. The increase of CD signal at 280 nm (from 2000 to about 4000 cm2 deg.dmole-1) in the case of sheared chromatin is not related to the loss of superstructure but to the structural changes of DNA inside the nucleosomal core which are always produced by shearing. These two correlated observations offer new sensitive probes of the integrity of any native or reconstituted chromatin.

Animals↗